When does maximum coronary blood flow occur?

Maximum coronary blood flow occurs during diastole due to the physiological dynamics of the cardiac cycle. During diastole, the heart muscle relaxes, allowing the coronary arteries to be filled with blood without obstruction. The aortic valve is closed during this phase, which means that blood does not flow into the aorta and instead is redirected into the coronary arteries.

Additionally, the myocardial oxygen demand is lower during diastole, allowing for optimal perfusion as circulation is less impeded. During systole, the heart muscles contract, and the increase in intramyocardial pressure can compress the coronary arteries, limiting blood flow. In contrast, faster heart rates (tachycardia) increase demand without providing adequate time for diastolic filling, which can further reduce coronary perfusion. Conversely, slower heart rates (bradycardia) can lead to longer diastolic phases, but this does not inherently maximize flow compared to normal rates. Thus, it is during diastole that coronary blood flow reaches its peak, ensuring efficient oxygen delivery to the myocardium.