An enlarged heart is a sign that the heart is overworked and is usually a symptom of an underlying disease or other factor that changes the way the heart functions. For example, a heart defect affecting the heart’s valves may mean that the heart is unable to pump oxygen-rich blood efficiently. Alternatively, in otherwise healthy people, long periods of intense exercise increases the demand for oxygen throughout the body, causing the heart to pump more blood. Either way, the heart has to work harder to satisfy the body’s demands.

Over time, this higher work level can cause the heart to enlarge as the chambers grow to allow more blood to be processed. Depending upon the nature of the enlargement, the heart can become stretched to its limit, like a taut rubber band. Among children and adolescents, an enlarged heart can lead to sudden cardiac death.

Medically, an enlarged heart is known as cardiomegaly or a hypertrophic heart. If just the left ventricle is enlarged, the condition is known as left ventricular hypertrophy. This can occur as a result of diseases or conditions that place extra stress on the left ventricle, which is the heart's main pumping chamber.

Hypertrophic cardiomyopathy is another condition in which the heart is enlarged. In this condition, there is an abnormal growth of muscle fibers on the heart, causing it to enlarge. This is generally considered a genetic disorder and can cause sudden cardiac death in seemingly healthy young individuals.

Heart enlargement can be pathological (related to significant heart disease) or physiological (related to exercise or other physical activity). Any sustained condition or activity that makes the heart work harder can enlarge it, including:

• Heart failure
  
  
• Coronary artery disease
  
  
• Valve disease
  
  
• High blood pressure (hypertension)
  
  
• Obesity
  
  
• Coronary artery spasm
  
  
• Cardiac ischemia
  
  
• Thyroid disease
  
  
• Severe anemia
  
  
• Excess iron or protein build-up in the body
  
  
• Excessive alcohol use
  
  
• Obstructive sleep apnea

Additionally, a small number of patients have an enlarged heart with no known cause (idiopathic).

Another condition, sometimes referred to as “athlete’s heart,” can occur in high-level athletes who engage in regular, sustained and often intense exercise. In most cases, this is not a medically significant or dangerous condition for them. Some studies, however, have shown that even among elite athletes, an enlarged heart may raise the risk for heart failure. Athletes at all levels are recommended to undergo regular physical exams to rule out hidden or underlying heart defects.