Cardiac Cycle
The cardiac cycle refers to the sequence of events that occur during one heartbeat.
Duration: ~0.8 seconds (at 75 bpm)
Phases of the Cardiac Cycle:
1. Atrial Systole (0.1 sec)
Atria contract
Blood pushed into ventricles
AV valves (mitral/tricuspid) are open
Ventricles are relaxed
2. Ventricular Systole (0.3 sec)
Isovolumetric Contraction (all valves closed)
Pressure builds, no volume change
Ventricular Ejection
Semilunar valves (aortic/pulmonary) open
Blood is ejected into the aorta and pulmonary artery
3. Diastole (0.4 sec)
Isovolumetric Relaxation
All valves closed
Ventricles relax, pressure falls
Ventricular Filling
AV valves open
Blood flows from atria to ventricles
Passive filling first, then active filling via atrial systole