Coronary blood flow.

1. Coronary blood flow is approximately 250 mL/min and proceeds from the epicardium to the endocardium. 2. The heart is perfused entirely by the right and left coronary arteries. 3. Most of the venous return from the heart is through the coronary sinus, which opens directly into the right atrium. 4. A small amount of myocardial venous drainage empties directly into the cardiac chambers through the Thebesian veins. 5. During systole, myocardial contraction produces sufficient pressure to prevent perfusion. Therefore, the majority of perfusion occurs during diastole (70 – 80%). a. Coronary Perfusion Pressure = Diastolic Pressure – LVEDP 6. The myocardium has a very high degree of oxygen extraction (65%). 7. Myocardial oxygen demand in the most important factor determining coronary blood flow.