Cardiomegaly is the medical term for enlargement of the heart muscle, explains WebMD. In most cases, the enlargement results from coronary artery disease or high blood pressure, but there are numerous other causes, such as viral infections, pregnancy, alcohol or cocaine abuse, HIV and kidney disease.
In many cases, it is unclear what caused a patient's heart to enlarge, notes WebMD. Regardless of the specific cause of cardiomegaly, heart enlargement occurs when the heart muscle tissue becomes damaged. Once the enlargement reaches a certain point, the heart becomes less effective at pumping blood, ultimately leading to congestive heart failure. Congestive heart failure occurs when the kidneys retain fluid and salt in response to the reduced pumping ability of the heart. Then, this fluid builds up in various areas throughout the body, such as in the lungs, ankles and feet.
The most common form of cardiomegaly is dilated cardiomyopathy, which results when both sides, or ventricles, of the heart stretch, explains WebMD. This stretching of the tissue causes the ventricles to become thinner. Another form involves thickening of the left ventricle, most often due to high blood pressure. As a general rule, it is harder for the heart to pump blood when the enlargement results in thinning of the tissue than it is when the enlargement is a product of ventricular thickening.