Many heart disease may be undetected at rest and only cause symptoms during exertion. In addition, many people have symptoms with exertion that are felt to be due to cardiac disease when the heart is perfectly normal. An exercise test may help in diagnosing milder cardiac abnormalities, assess how good or bad the heart function is in a person with a weak heart muscle, and relieve anxiety in people with exertional symptoms who have normal hearts.
Exercise increases the work of the heart.
More work requires more blood for the heart muscle. Narrowing of the coronary arteries reduces the amount of blood that can flow through the vessels. The lack of enough blood to the heart muscle causes specific changes in the electrocardiogram. Recording the electrocardiogram before, during, and after exercise shows these changes. In addition, if there is narrowing of the valves or the heart muscle is weak, the heart will be limited in its ability to pump enough blood to allow significant exercise.