The powerful heart muscle requires a good supply of oxygen and energy to keep it working efficiently. It therefore has its own special circulation, called the coronary circulation. The coronary arteries lead directly from branches located just above the aortic valve, so receiving the most freshly oxygenatedjust back from the lungs.
Obstruction of one or more of these coronary arteries causes what is known as a heart attack, or myocardial infarction. You may also hear it referred to as a coronary thrombosis because the blockage is often (but not always) caused by aclot, or thrombus. Clotting is also encouraged by thickening of artery walls by fatty deposits (atherosclerosis). The thrombus results in a severe lack of , and therefore lack of oxygen, to part of the heart muscle, which dies (infarction). Fortunately all the coronary arteries branch and interlink, so that blood can often reach the affected area by an alternative, unblocked, route. From the heart muscle the blood returns into the heart chambers along two routes. One is through the network of coronary veins, which join together and travel back roughly along the paths of the arteries, to enter the right atrium. The second route is through tiny veins, the venae cordis minimae, running through the heart muscle and emptying directly into the main chambers within.
The blood supply to the heart is obviously of vital importance, because without it the heart muscle will not function. Lack of oxygen in the heart muscle causes severe pain (the pain of a heart attack or, less seriously, angina pectoris). In angina pectoris, also called angina of effort, the coronary arteries cannot supply enough blood to the heart muscle to meet the body’s demand for extra blood during physical exercise, excitement or even after a big meal. Pain is usually felt in the chest, neck, shoulder or arms (particularly the left arm). As well as being caused by coronary artery disease – usually resulting from atherosclerosis – angina pectoris may be a symptom of high blood pressure, anaemia or valvular heart disease. The symptoms can be relieved by taking drugs such as glyceryl trinitrate, preferably before any strenuous activity. In other cases the heart gradually loses efficiency, resulting in heart failure. Or the heart may be unable to conduct the electrical impulses neccess-ary to co-ordinate its pumping action, which leads to irregularities of heart rate and rhythm known as arrhythmias. Several serious disorders, particularly coronary thrombosis, can lead to complete cessation of heartbeat – a cardiac arrest. Unless the heart is restarted within a minute or two by emergencyprocedures, it will never beat again.