During which phase of the cardiac cycle do coronary vessels primarily dilate to increase blood flow to the heart muscle?

During which phase of the cardiac cycle do coronary vessels primarily dilate to increase blood flow to the heart muscle?

• A. Ventricular systole
• B. Atrial systole
• C. Ventricular diastole
• D. Isovolumetric contraction

Answer: (C)

The heart’s own blood supply is governed by the need to match oxygen delivery with metabolic demand, and the timing of coronary perfusion is tied to the heart’s mechanical state. When the ventricles contract, intramyocardial pressure rises and compresses the coronary vessels, especially the subendocardial vessels, which limits blood flow to the heart muscle. As the ventricles relax, that pressure falls and the coronary vessels dilate to allow more blood to reach the myocardium. This dilation and increased flow occur primarily during ventricular diastole, the phase of relaxation. The heart muscle benefits from this period of lower pressure and open, dilated vessels, with local metabolic signals (like adenosine and CO2) further promoting vasodilation to meet the resting and active needs of the tissue. During ventricular systole and the isovolumetric contraction phase, the myocardium is contracting and the vessels are compressed, so coronary flow is reduced despite any vasodilatory signals. Atrial systole contributes little to coronary perfusion compared with diastole.

The heart’s own blood supply is governed by the need to match oxygen delivery with metabolic demand, and the timing of coronary perfusion is tied to the heart’s mechanical state. When the ventricles contract, intramyocardial pressure rises and compresses the coronary vessels, especially the subendocardial vessels, which limits blood flow to the heart muscle. As the ventricles relax, that pressure falls and the coronary vessels dilate to allow more blood to reach the myocardium.

This dilation and increased flow occur primarily during ventricular diastole, the phase of relaxation. The heart muscle benefits from this period of lower pressure and open, dilated vessels, with local metabolic signals (like adenosine and CO2) further promoting vasodilation to meet the resting and active needs of the tissue.

During ventricular systole and the isovolumetric contraction phase, the myocardium is contracting and the vessels are compressed, so coronary flow is reduced despite any vasodilatory signals. Atrial systole contributes little to coronary perfusion compared with diastole.