In some people, an enlarged heart causes no signs or symptoms. Others may have these signs and symptoms:

• Shortness of breath
• Abnormal heart rhythm (arrhythmia)
• Swelling (edema)

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 enlarges and becomes weak for unknown reasons (idiopathic).

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 (atria).

• 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), connective tissue disorders, certain medications or radiation treatments for cancer, your heart may enlarge.
• Disease of the heart muscle (cardiomyopathy). As this thickening and stiffening of heart muscle progresses, your heart may enlarge to try to pump more blood to your body.
• High blood pressure in the artery connecting 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 (pericardium) that contains your heart may cause your heart to appear enlarged on a chest X-ray.
• 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.

You may have a greater risk of developing an enlarged heart if you have any of the following risk factors:

• High blood pressure. Having a blood pressure measurement higher than 140/90 millimeters of mercury puts you at an increased risk of developing an enlarged heart.
• A family history of enlarged hearts or cardiomyopathy. If an immediate family member, such as a parent or sibling, has had an enlarged heart, you may be more susceptible to developing the condition.
• Blocked arteries in your heart (coronary artery disease). With this condition, fatty plaques 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.
• Congenital heart disease. If you're born with a condition that affects the structure of your heart, you may be at risk of developing an enlarged heart.
• Heart valve disease. The heart has four valves — aortic, mitral, pulmonary and tricuspid — that open and close to direct blood flow through your heart. Conditions that damage the valves may cause the heart to enlarge.
• Heart attack. Having a heart attack increases your risk of developing an enlarged heart.

The risk of complications from an enlarged heart depends on the part of the heart that is enlarged and the cause.

Complications of an enlarged heart can include:

• Heart failure. One of the most serious types of enlarged heart, an enlarged left ventricle increases the risk of heart failure. In heart failure, your heart muscle weakens, and the ventricles stretch (dilate) to the point that the heart can't pump blood efficiently throughout your body.
• Blood clots. Having an enlarged heart may make you more susceptible to forming blood clots in the lining of your heart. If clots enter your bloodstream, they can block blood flow to vital organs, even causing a heart attack or stroke. Clots that develop on the right side of your heart may travel to your lungs, a dangerous condition called a pulmonary embolism.
• Heart murmur. For people who have an enlarged heart, two of the heart's four valves — the mitral and tricuspid valves — may not close properly because they become dilated, leading to a backflow of blood. This flow creates sounds called heart murmurs. Although not necessarily harmful, heart murmurs should be monitored by your doctor.
• Cardiac arrest and sudden death. Some forms of an enlarged heart can lead to disruptions in your heart's beating rhythm. Heart rhythms too slow to move blood or too fast to allow the heart to beat properly can result in fainting or, in some cases, cardiac arrest or sudden death.