Designed and illustrated by Charlie James Content by Bradley Chambers/CJ
The Cardiac Cycle
This interactive resource allows you to explore the events of the cardiac cycle. Click the round buttons to learn about the events at each point in the cycle. Click the boxes at the bottom to explore different elements of the cardiac cycle. Text in blue can be clicked to reveal more information. Click the question mark to try the self-assessment quiz.
ANATOMY
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Atrial systole
Atrial contraction forces a small amount of extra blood into the ventricles. This blood flows through the atrio-ventricular valves. These valves allow blood to enter the ventricles, but stop blood from returning into the atria. On the right side of the heart, the AV valve has three cusps [or flaps] and is known as the tricuspid valve. On the left side of the heart, the valve has two cusps and is sometimes known as the bicuspid valve. It may also be referred to as the mitral valve [as it resembles an upside down 'mitre' - the hat that a bishop wears].
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular contraction
This first phase of ventricular contraction pushes the AV valves shut, but doesn't generate enough pressure to open the semilunar valves. The semilunar valves guard the entrance of the great arteries, ensuring that blood can leave the heart, but doesn't flow back into the ventricles. These valves are named 'semilunar' as their cusps are cresecent-shaped, like a moon. Each valve is named after the artery they guard, with a pulmonary valve on the right and an aortic valve on the left. Closure of the AV valves produces the S1 sound/'lub'.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Ventricular systole
The ventricular walls contract, increasing pressure in the ventricles. Once this pressure exceeds the pressure in the arteries, the semilunar valves open and blood is ejected from the heart. As pressure in the ventricles increases, so does the risk of the AV valves prolpasing and blood being regurgitated into the atria. To prevent this, tendinous cords [the chordae tendinae] pass from the valve cusps to papillary muscles on the ventricular wall. Contraction of a papillary muscle pulls the chordae tendinae tight, holding the valve cusps in place.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular relaxation
As the ventricles relax, the pressure inside of them drops. Blood flows into the cusps of the semilunar valves, snapping them shut. Because blood returning to the semilunar valves is under relatively low pressure, these valves don't need to be reinforced with chordae tendinae. At this stage, blood also begins flowing intro the atria from the systemic veins and pulmonary veins. Closure of the semilunar valves creates the second S2 sound/'dub'.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Late diastole
Both sets of chambers are relaxed and fill passively with blood. Deoxygenated blood flows into the right atrium via the terminal systemic veins, the superior and inferior venae cavae. Oxygenated blood flows into the left atrium via the pulmonary veins.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
P wave
The first positive deflection on an ECG, the P wave reflects depolarisation of the atria. This wave of depolarisation originates from the sino-atrial node in the wall of the right atrium.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
P-Q or P-R interval
This stage represents conduction of the signal through the AV node and into the AV bundle. The AV node delays the signal. This ensures full atrial contraction/ventricular filling before the depolarisation and contraction of the ventricles.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Q wave
This negative deflection represents the depolarisation of the interventricular septum [the wall between the ventricles]. The impulse travels down a pair of left and right bundle branches.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
R wave
This prominent upward deflection represents early ventricular depolarisation.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
S wave
This small downward deflection represents the wave of depolarisation travelling up the Purkinje fibres.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
S-T segment
This segment represents the period between ventricular depolarisation and repolarisation.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
T wave
This positive deflection represents ventricular repolarisation.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Atrial systole
Atrial contraction increases pressure within the atria. A small amount of extra blood is expelled into the ventricles.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular contraction
Increasing pressure in the ventricles closes the atrio-ventricular valves, however the pressure isn't great enough to open the semilunar valves.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Ventricular systole
The ventricular walls contract, increasing pressure in the ventricles. Once this pressure exceeds the pressure in the aorta, the semilunar valves open and blood is ejected from the heart.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular relaxation
As the ventricles relax, the pressure inside of them drops. Higher pressure arterial blood flows into the cusps of the semilunar valves, snapping them shut. Pressure in the ventricles continues lowering, but remains higher than in the atria, keeping the atrio-ventricular valves shut.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Late diastole
Pressure in the ventricles becomes slightly lower than in the atria, allowing the atrio-ventricular valves to open. Blood flows into all four chambers, and pressure is roughly equal across the heart.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Cardiac Cycle: The Quiz
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
ST segment
PQ interval
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
ST segment
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
Not sure? Click the button to review the relevant page
P wave
The first positive deflection on an ECG, the P wave reflects depolarisation of the atria. This wave of depolarisation originates from the sino-atrial node in the wall of the right atrium.
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
T wave
This positive deflection represents ventricular repolarisation.
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Isometric ventricular contraction
This first phase of ventricular contraction pushes the AV valves shut, but doesn't generate enough pressure to open the semilunar valves. The semilunar valves guard the entrance of the great arteries, ensuring that blood can leave the heart, but doesn't flow back into the ventricles. These valves are named 'semilunar' as their cusps are cresecent-shaped, like a moon. Each valve is named after the artery they guard, with a pulmonary valve on the right and an aortic valve on the left. Closure of the AV valves produces the S1 sound.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Q wave
This negative deflection represents the depolarisation of the interventricular septum [the wall between the ventricles]. The impulse travels down a pair of left and right bundle branches.
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Atrial systole
Atrial contraction forces a small amount of extra blood into the ventricles. This blood flows through the atrio-ventricular valves. These valves allow blood to enter the ventricles, but stop blood from returning into the atria. On the right side of the heart, the AV valve has three cusps [or flaps] and is known as the tricuspid valve. On the left side of the heart, the valve has two cusps and is sometimes known as the bicuspid valve. It may also be referred to as the mitral valve [as it resembles an upside down 'mitre' - the hat that a bishop wears].
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
The Cardiac Cycle
Anartomy
Created on January 13, 2023
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Transcript
The Cardiac Cycle
Start
Designed and illustrated by Charlie James Content by Bradley Chambers/CJ
The Cardiac Cycle
This interactive resource allows you to explore the events of the cardiac cycle. Click the round buttons to learn about the events at each point in the cycle. Click the boxes at the bottom to explore different elements of the cardiac cycle. Text in blue can be clicked to reveal more information. Click the question mark to try the self-assessment quiz.
ANATOMY
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Atrial systole
Atrial contraction forces a small amount of extra blood into the ventricles. This blood flows through the atrio-ventricular valves. These valves allow blood to enter the ventricles, but stop blood from returning into the atria. On the right side of the heart, the AV valve has three cusps [or flaps] and is known as the tricuspid valve. On the left side of the heart, the valve has two cusps and is sometimes known as the bicuspid valve. It may also be referred to as the mitral valve [as it resembles an upside down 'mitre' - the hat that a bishop wears].
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular contraction
This first phase of ventricular contraction pushes the AV valves shut, but doesn't generate enough pressure to open the semilunar valves. The semilunar valves guard the entrance of the great arteries, ensuring that blood can leave the heart, but doesn't flow back into the ventricles. These valves are named 'semilunar' as their cusps are cresecent-shaped, like a moon. Each valve is named after the artery they guard, with a pulmonary valve on the right and an aortic valve on the left. Closure of the AV valves produces the S1 sound/'lub'.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Ventricular systole
The ventricular walls contract, increasing pressure in the ventricles. Once this pressure exceeds the pressure in the arteries, the semilunar valves open and blood is ejected from the heart. As pressure in the ventricles increases, so does the risk of the AV valves prolpasing and blood being regurgitated into the atria. To prevent this, tendinous cords [the chordae tendinae] pass from the valve cusps to papillary muscles on the ventricular wall. Contraction of a papillary muscle pulls the chordae tendinae tight, holding the valve cusps in place.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular relaxation
As the ventricles relax, the pressure inside of them drops. Blood flows into the cusps of the semilunar valves, snapping them shut. Because blood returning to the semilunar valves is under relatively low pressure, these valves don't need to be reinforced with chordae tendinae. At this stage, blood also begins flowing intro the atria from the systemic veins and pulmonary veins. Closure of the semilunar valves creates the second S2 sound/'dub'.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Late diastole
Both sets of chambers are relaxed and fill passively with blood. Deoxygenated blood flows into the right atrium via the terminal systemic veins, the superior and inferior venae cavae. Oxygenated blood flows into the left atrium via the pulmonary veins.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
P wave
The first positive deflection on an ECG, the P wave reflects depolarisation of the atria. This wave of depolarisation originates from the sino-atrial node in the wall of the right atrium.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
P-Q or P-R interval
This stage represents conduction of the signal through the AV node and into the AV bundle. The AV node delays the signal. This ensures full atrial contraction/ventricular filling before the depolarisation and contraction of the ventricles.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Q wave
This negative deflection represents the depolarisation of the interventricular septum [the wall between the ventricles]. The impulse travels down a pair of left and right bundle branches.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
R wave
This prominent upward deflection represents early ventricular depolarisation.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
S wave
This small downward deflection represents the wave of depolarisation travelling up the Purkinje fibres.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
S-T segment
This segment represents the period between ventricular depolarisation and repolarisation.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
T wave
This positive deflection represents ventricular repolarisation.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Atrial systole
Atrial contraction increases pressure within the atria. A small amount of extra blood is expelled into the ventricles.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular contraction
Increasing pressure in the ventricles closes the atrio-ventricular valves, however the pressure isn't great enough to open the semilunar valves.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Ventricular systole
The ventricular walls contract, increasing pressure in the ventricles. Once this pressure exceeds the pressure in the aorta, the semilunar valves open and blood is ejected from the heart.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Isometric ventricular relaxation
As the ventricles relax, the pressure inside of them drops. Higher pressure arterial blood flows into the cusps of the semilunar valves, snapping them shut. Pressure in the ventricles continues lowering, but remains higher than in the atria, keeping the atrio-ventricular valves shut.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Late diastole
Pressure in the ventricles becomes slightly lower than in the atria, allowing the atrio-ventricular valves to open. Blood flows into all four chambers, and pressure is roughly equal across the heart.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
ANATOMY
Cardiac Cycle: The Quiz
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
ST segment
PQ interval
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
ST segment
Not sure? Click the button to review the relevant page
Cardiac Cycle: The Quiz
Not sure? Click the button to review the relevant page
P wave
The first positive deflection on an ECG, the P wave reflects depolarisation of the atria. This wave of depolarisation originates from the sino-atrial node in the wall of the right atrium.
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
T wave
This positive deflection represents ventricular repolarisation.
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Isometric ventricular contraction
This first phase of ventricular contraction pushes the AV valves shut, but doesn't generate enough pressure to open the semilunar valves. The semilunar valves guard the entrance of the great arteries, ensuring that blood can leave the heart, but doesn't flow back into the ventricles. These valves are named 'semilunar' as their cusps are cresecent-shaped, like a moon. Each valve is named after the artery they guard, with a pulmonary valve on the right and an aortic valve on the left. Closure of the AV valves produces the S1 sound.
Click along the timeline to learn more about what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Q wave
This negative deflection represents the depolarisation of the interventricular septum [the wall between the ventricles]. The impulse travels down a pair of left and right bundle branches.
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Atrial systole
Atrial contraction forces a small amount of extra blood into the ventricles. This blood flows through the atrio-ventricular valves. These valves allow blood to enter the ventricles, but stop blood from returning into the atria. On the right side of the heart, the AV valve has three cusps [or flaps] and is known as the tricuspid valve. On the left side of the heart, the valve has two cusps and is sometimes known as the bicuspid valve. It may also be referred to as the mitral valve [as it resembles an upside down 'mitre' - the hat that a bishop wears].
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY
Atrial Systole
Contraction of the atria
Click along the timeline to learn more what happens at each stage
Ventricular systole
Ventricular diastole
Atrial systole
Atrial systole
Click the buttons below to explore different elements of the cardiac cycle
pressure
conduction
Blood flow
ANATOMY