The heart feeds itself mostly in the pauses between beats
When the heart muscle squeezes, the pressure inside it crushes the small vessels that run into its own walls, and blood flow in the innermost layer stops. So the heart does most of its own refuelling during relaxation, in the brief gap before the next contraction, through a network with almost no backup routes.
The coronary circulation is the heart's private blood supply. Two coronary arteries leave the aorta just above its valve, from two of three small bulges in the vessel wall; the third bulge usually produces nothing. The left artery serves the left atrium and ventricle and the wall between the ventricles, splitting into the circumflex branch and the larger left anterior descending artery. The right artery feeds the right atrium, parts of both ventricles and the electrical conduction system. Cardiac veins then collect the used blood, most of it draining through the coronary sinus into the right atrium.
Elsewhere in the body, arteries often join up so that one blockage can be bypassed, as in the palm of the hand. In the heart such junctions are tiny, which is why the coronaries are treated as functional end arteries. A sudden blockage usually kills the muscle that vessel supplied, which is a heart attack. Only when a fatty plaque grows slowly do the small connections have time to enlarge and take over.
Anatomists classify hearts by which artery supplies the posterior descending branch at the back of the septum. About 70 percent of people are right-dominant, 20 percent co-dominant and 10 percent left-dominant. The detail has consequences: one papillary muscle anchoring the mitral valve usually gets blood from two arteries, while its partner relies on just one, so a blockage there is more likely to leave the valve leaking backward.
The squeeze problem mainly affects vessels buried inside the muscle; those running along the surface stay open, and flow in the right coronary never drops to zero because pressure in the right ventricle is lower. Healthy arteries adjust their width to match the heart's oxygen needs, a process modellers now simulate layer by layer. When supply falls short, brief shortage causes the chest pain called angina, and prolonged moderate shortage can weaken contraction, a state termed myocardial hibernation.
Source: Coronary circulation
