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What happens during systole and diastole in the cardiac cycle?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

The cardiac cycle consists of two primary phases, systole and diastole, which coordinate the pumping of blood through the heart.12

Systole

Systole is the period of contraction of the heart muscle.1
* Ventricular Systole: Lasting approximately 0.3 to 0.4 seconds, this phase involves the contraction of the ventricles, which ejects blood into the aorta and pulmonary trunk. During this time, arterial blood pressure reaches its peak, known as systolic blood pressure.1
* Atrial Systole: This occurs toward the end of ventricular diastole, completing the filling of the ventricles.1

Diastole

Diastole is the period of relaxation of the heart muscle, during which the heart chambers fill with blood.2
* Filling Phase: Initially, both the atria and ventricles are in diastole, allowing for rapid filling of the ventricles.2
* Pressure: During this phase, arterial blood pressure decreases to its minimum, known as diastolic blood pressure.2

These alternating phases ensure the efficient, rhythmic movement of blood throughout the body to meet metabolic demands.3