Some hearts that have been examined after a fatal heart attack reveal no actual obstruction of the blood vessel, only a narrowing of the artery. In this circumstance, how did the infarction develop? It is difficult, if not impossible, to know exactly what happened, but this may be what occurs. Most of us are familiar with the function of gasoline engines. Many of us have at one time or another tinkered with our engines and are aware that if the gas line between the fuel tank and the fuel pump were kinked difficulty would arise. The engine might run satisfactorily at idling speed, or even when the automobile was running at 20 or 30 miles per hour. But at some critical point, say 40 miles per hour, enough gas would not pass through the obstruction and the engine would falter.In the automobile there is no great problem because if the engine falters the car merely slows down. In the human mechanism, however, a different result may occur. If a person were doing heavy work, the muscles in his arms and legs would be burning up oxygen and food at a rapid rate. These substances are supplied by the blood stream, and the normal course of events is for the heart to pump a greater amount of blood into the blood vessels to supply the working muscles. When the heart pumps a greater quantity of blood, it, too, is working harder and requires a greater amount of oxygen and food. These energy substances must be delivered through the coronary arteries. If the coronary arteries are narrowed and are unable to deliver adequate amounts of food and oxygen to the heart muscle during total body exercise, and if the total body work and the demands upon the heart continue despite inadequate nourishment of the heart muscle, that portion of the heart muscle supplied by a narrowed coronary artery could, figuratively speaking, burn itself out.We believe that when the heart receives inadequate food and oxygen, it sends a signal to our conscious mind in the form of chest pain. If the period of deficient blood flow is of short duration, no damage will occur to the heart muscle. If this deficiency is prolonged beyond a critical period, the heart tissue will die. This, again, is essentially the difference between angina pectoris and a myocardial infarction. Angina pectoris is known to the patient as a chest pain that is usually of just several minutes duration. Although it may occur when a person is at rest, it usually happens when a person is active or after he has eaten a heavy meal. The person who has the pain usually stops what he is doing, or lies down, or takes a nitroglycerine tablet and within a few minutes the pain is relieved. When the person stopped walking, he decreased the demands that his leg muscles were placing on his heart and the heart could rest temporarily. This is probably why the pain stopped. When a person takes a nitroglycerine tablet, the drug temporarily increases the nourishment of the heart and, again, the pain stops. If the pain persists for many minutes or hours despite rest or nitroglycerine, it is likely that a complete occlusion has occurred and actual muscle death and myocardial infarction are in process.*10/309/5*