What happens during diastole in the cardiac cycle?
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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, diastole is the period of relaxation of the heart muscle, which allows the heart chambers to fill with blood.12
Key events during this phase include:
- Chamber Filling: Initially, both the atria and ventricles are in diastole. This facilitates a period of rapid ventricular filling, followed by a brief atrial contraction (atrial systole) that forces additional blood into the ventricles.12
- Pressure Changes: As the ventricles relax following the ejection of blood, the pressure within them falls. Simultaneously, arterial blood pressure decreases to its minimum level, known as diastolic blood pressure.12
- Heart Sounds: The transition into diastole is marked by the second heart sound (S2), produced by the closure of the aortic and pulmonary valves. Additionally, the third heart sound (S3) may occur during the early, rapid filling phase of diastole, while the fourth heart sound (S4) can occur late in diastole during atrial contraction.2
Diastole is the longer of the two phases in the cardiac cycle, providing the heart necessary time to rest between contractions.2