Most commonly, a myocardial infarction is the direct consequence of coronary atherosclerosis, or hardening of the arteries. The blocked arteries stop blood flow to the heart tissue and deprive the cells of necessary oxygen. Small areas of heart muscle may sustain damage, resulting in a scar; this may even occur without the individual experiencing significant symptoms. If larger areas of the heart are deprived of oxygen or if the cells that conduct the primary electrical impulses are within an area where blood flow is decreased, the heart may beat irregularly or even stop beating altogether. It is not unusual for sudden cardiac death to be the first symptom of coronary artery disease.

Fitness and Diving Issue

Cardiovascular events cause 20 to 30 percent of all deaths that occur while scuba diving. For many people, the real problem is that the first sign of coronary artery disease is a heart attack. The only realistic approach is to recommend appropriate measures to prevent the development of coronary atherosclerosis and to encourage regular medical evaluations for those individuals at risk.

Prudent diet and regular exercise should be habitual for divers. Older individuals and divers who have a family history of myocardial infarctions, especially at an early age, should receive appropriate evaluations to detect early signs of coronary artery disease.

Individuals who have experienced previous heart attacks are at risk for additional cardiac events in the future, and damaged heart tissue may have compromised cardiac function. The damaged left ventricle may not be able to pump blood as efficiently as it could prior to the MI.

Regardless of whether an individual has had a revascularization procedure (see "Coronary Artery Bypass Grafting"), strict criteria must be met prior to an individual's safe return to diving. After a period of healing - six to 12 months is recommended - an individual should undergo a thorough cardiovascular evaluation, which includes an exercise stress test. The individual should perform at a level of 13 mets (stage 4 on Bruce protocol). This is a fairly brisk level of exercise, equating to progressively running faster until the patient reaches a pace that is slightly faster than running an 8-minue mile (for a very brief period of time). Performance at that level without symptoms or EKG changes indicates normal exercise tolerance.