Factors ensuring that ventricular muscle has an adequate oxygen supply include the

A. False  Coronary arteries are functional ‘end arteries’ and have few anastomotic connections; sudden occlusion of an artery usually leads to local muscle death.

B. False  Coronary vessels are compressed by the contracting myocardium in systole.

C. True  The extraction rate is about 75 per cent.

D. False  Reflex vasodilatation is not important in regulating coronary blood flow.

E. True  The rise in metabolic activity in the exercising heart provides the vasodilator metabolites which adapt coronary flow to supply myocardial oxygen needs.