Coronary microcirculation: Physiology and mechanics

The heart is unique among other organs in that coronary arterial flow is exclusively diastolic and venous outflow is systolic. That is, arterial blood flows into intramyocardial coronary vessels during diastole and the stored blood is squeezed out mostly to epicardial veins and partly to the proximal arteries during the subsequent systole. Furthermore, coronary vessels function as highly organized flow regulators to match local blood flows with myocardial energy demands to support the viability of the heart. In this review, we first summarize the intramyocardial microvascular dynamics along with the description of a hierarchical system of coronary microvessels. Then, the spatial heterogeneity of blood supply to myocardium is demonstrated.