Causes

An enlarged heart can be caused by conditions that cause your heart to pump harder than usual or that damage your heart muscle. Sometimes the heart gets larger and becomes weak for unknown reasons. This is known as idiopathic cardiomegaly.

A heart condition you're born with (congenital), damage from a heart attack or an abnormal heartbeat (arrhythmia) can cause your heart to enlarge. Other conditions associated with an enlarged heart include:

• High blood pressure. Your heart may have to pump harder to deliver blood to the rest of your body, enlarging and thickening the muscle.

  High blood pressure can cause the left ventricle to enlarge, causing the heart muscle eventually to weaken. High blood pressure may also enlarge the upper chambers of your heart.

• Heart valve disease. Four valves in your heart keep blood flowing in the right direction. If the valves are damaged by conditions such as rheumatic fever, a heart defect, infections (infectious endocarditis), an irregular heartbeat (atrial fibrillation) connective tissue disorders, certain medications or radiation treatments for cancer, your heart may enlarge.
• Cardiomyopathy. This disease of the heart makes it harder for your heart to pump blood throughout your body. As it progresses, your heart may enlarge to try to pump more blood.
• High blood pressure in the artery that connects your heart and lungs (pulmonary hypertension). Your heart may need to pump harder to move blood between your lungs and your heart. As a result, the right side of your heart may enlarge.
• Fluid around your heart (pericardial effusion). Accumulation of fluid in the sac that contains your heart may cause your heart to appear enlarged on a chest X-ray.
• Blocked arteries in your heart (coronary artery disease). With this condition, fatty plaque in your heart arteries obstruct blood flow through your heart vessels, which can lead to a heart attack. When a section of heart muscle dies, your heart has to pump harder to get adequate blood to the rest of your body, causing it to enlarge.
• Low red blood cell count (anemia). Anemia is a condition in which there aren't enough healthy red blood cells to carry adequate oxygen to your tissues. Untreated, chronic anemia can lead to a rapid or irregular heartbeat. Your heart must pump more blood to make up for the lack of oxygen in the blood.
• Thyroid disorders. Both an underactive thyroid gland (hypothyroidism) and an overactive thyroid gland (hyperthyroidism) can lead to heart problems, including an enlarged heart.
• Excessive iron in the body (hemochromatosis). Hemochromatosis is a disorder in which your body doesn't properly metabolize iron, causing it to build up in various organs, including your heart. This can cause an enlarged left ventricle due to weakening of the heart muscle.
• Rare diseases that can affect your heart, such as amyloidosis. Amyloidosis is a condition in which abnormal proteins circulate in the blood and may be deposited in the heart, interfering with your heart's function and causing it to enlarge.