BRAINCAKEThe Cardiac Cycle
The cardiac cycle is the sequence of events in one complete heartbeat. It has three stages. Both sides of the heart go through the stages at the same time.
1. Cardiac diastole. The atria and ventricles are all relaxed. Blood flows from the veins into the atria. As the atria fill, their pressure rises above that in the ventricles, so the atrioventricular valves open and blood flows passively into the ventricles. The semilunar valves are closed, because pressure in the arteries is higher than in the ventricles.
2. Atrial systole. The atria contract, pushing the remaining blood into the ventricles. The ventricles are relaxed.
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More in The Heart
- Structure of the Human Heart
- Blood Flow through the Heart
- Contraction of Cardiac Muscle
- Control of the Heartbeat
- Electrocardiograms
- Electrical and Pressure Changes in the Heart
All 7 lessons in The Heart · All Edexcel AS-level Biology topics