the blood supply to the cardiac muscle, carried by the intercommunicating arteries and veins that run throughout the myocardium.

In man, arterial blood is supplied mainly by the right and left coronary arteries, which begin at the base of the aorta. There are three types of blood supply—right coronary, left coronary, and general—which in some measure determine the nature of the pathology of the coronary circulation in the event of disease of the heart vessels. The coronary veins are both larger and greater in number than the arteries. The veins empty into the right atrium. The principal arterial and venous trunks are connected by a well-developed network of anastomoses, which facilitates collateral (shunt) circulation in cases of impairment of blood supply to the heart.

The great intensity of the blood supply to the myocardium is provided by a dense network of capillaries (approximately twice the number per unit volume than in the skeletal muscles). The level of the coronary circulation in a healthy body corresponds exactly to the force and frequency of the heartbeat. It is regulated both by physical factors (for example, blood pressure in the aorta) and by neural and humoral mechanisms. Coronary circulation is influenced by physical and mental condition and by the degree and character of stress or load. It is sharply impaired by nicotine and certain factors that lead to atherosclerosis, hyper-tension, and cardiac ischemia, such as overstrain of the nervous system, negative emotions, improper nutrition, and the absence of constant physical excercise. Coronary insufficiency and disturbances of coronary circulation are among the most frequent causes of death in economically developed countries, and there-fore their prevention and treatment (mainly of infarction) are the most pressing problems of modern medicine.