The heart requires its own constant supply of oxygen and nutrients, like any muscle in the body. The heart has four main arteries, two of them large, branching arteries that deliver oxygenated blood to the heart muscle. If one of these arteries or branches becomes blocked suddenly, a portion of the heart is starved of oxygen, a condition called cardiac ischemia. If cardiac ischemia lasts too long, the starved heart tissue dies. This is a heart attack, otherwise known as a myocardial infarction -- literally, death of heart muscle. “Most heart attacks occur during several hours -- so never wait to seek help if you think a heart attack is beginning. In some cases there are no symptoms at all, but most heart attacks produce some chest pain. Other signs of a heart attack include shortness of breath, dizziness, faintness, or nausea. The pain of a severe heart attack has been likened to a giant fist enclosing and squeezing the heart. If the attack is mild, it may be mistaken for heartburn. The pain may be constant or intermittent. Also, women are less likely to experience the classic symptoms of chest pain; rather, they may feel a sense of fullness in their chest or pain in their arm, neck, back or jaw.