Cardiac cycle
One cardiac cycle comprises electrical activation, coordinated filling and ejection, and valve movements driven by pressure differences.
Open interactive lesson & self-check ↗Cardiac cycle: four pressure-driven phases
Original conceptual SVG · scalableSequence and valve state are schematic. Cycle durations vary with heart rate and physiology.
Follow diastole
During ventricular relaxation and filling, atrioventricular valves are open when atrial pressure exceeds ventricular pressure. Semilunar valves remain closed.
Follow systole
As ventricular pressure exceeds atrial pressure the AV valves close. When ventricular pressure exceeds great-artery pressure, the outflow valve opens and ejection begins.
Relate heart sounds
S1 is associated with AV valve closure at the onset of ventricular systole. S2 is associated with semilunar valve closure near the end of ventricular ejection.
Reference and next reading
Explore the original curriculum and publisher-hosted resources for full-depth reading; this note is an original schematic introduction, not an exhaustive chapter.