When does filling of the coronary arteries primarily occur during the cardiac cycle?

Filling of the coronary arteries primarily occurs during ventricular diastole. During this phase of the cardiac cycle, the heart muscle relaxes, allowing the chambers to fill with blood. As the ventricles fill, the pressure within them decreases significantly. This decrease in pressure relative to the aorta allows blood to flow into the coronary arteries from the aorta.

The coronary arteries originate from the base of the aorta, just above the aortic valve. When the aortic valve closes at the end of systole, there is a small period when the pressure in the aorta is higher than in the relaxed ventricle, which facilitates blood flow back into the coronary arteries. This flow is crucial for supplying oxygen and nutrients to the heart muscle itself.

In contrast, during systole, when the heart actively contracts to pump blood out, the coronary arteries are compressed, and flow is reduced. Isovolumetric relaxation, while part of diastole, is a brief period in the cycle before the ventricles fully relax and fill with blood. Atrial contraction occurs later in diastole and is primarily responsible for pushing the last volume of blood into the ventricles, but it is not the primary phase for coronary filling. Thus, the