When do the coronary arteries fill with blood?

The coronary arteries fill with blood primarily during diastole, which is the phase of the cardiac cycle when the heart muscle relaxes following contraction. During this time, the aortic valve closes, preventing blood from flowing back into the heart, and the negative pressure created allows blood to flow into the coronary arteries that branch off the aorta.

Understanding this mechanism is essential for comprehending how the heart receives oxygen-rich blood. Since the coronary arteries are a low-pressure system, they are most effectively perfused when the heart is not actively contracting. In contrast, during systole, which is the contraction phase, the coronary arteries can be compressed, reducing blood flow.

This physiological detail is key to evaluating cardiac health, especially in conditions like coronary artery disease, where the supplied blood may become limited or insufficient during critical times, such as increased physical demand.