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What happens during systole in the cardiac cycle?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

During the cardiac cycle, systole refers to the period of contraction of the heart muscle. This process is essential for the efficient pumping of blood throughout the body.123

Ventricular Systole

Ventricular systole is the contraction of the ventricles, typically lasting 0.3 to 0.4 seconds. It begins with a brief period of contraction followed by an ejection phase, during which approximately 80 to 100 cc of blood is forced into the aorta and the pulmonary trunk. As the ventricles contract, the atrioventricular valves close to prevent backflow, creating the first heart sound. During this phase, arterial blood pressure rises to its peak, known as systolic blood pressure.14

Atrial Systole

Atrial systole occurs toward the end of ventricular diastole. The contraction of the atria completes the filling of the ventricles with blood before the ventricles themselves begin to contract. In an electrocardiogram, this phase is associated with the P wave, representing atrial depolarization.12