Diastole is the phase of the cardiac cycle when the heart muscles relax after contraction. During this time, the chambers of the heart, specifically the atria and ventricles, fill with blood. This process is essential for maintaining proper blood circulation throughout the body. In humans, diastole occurs after the heart pumps blood out to the lungs and the rest of the body during systole. The duration of diastole can vary based on factors like heart rate and overall cardiovascular health. Proper diastolic function is crucial for effective heart performance and overall well-being.