Cardiomegaly (sometimes megacardia or megalocardia) is a medical condition in which the heart is enlarged. As such, it is more commonly referred to simply as "having an enlarged heart".

Cardiomegaly is not a disease, but rather a condition that can result from a host of other diseases such as obesity or coronary artery disease. Cardiomegaly can be serious: depending on what part of the heart is enlarged, the patient can suffer from heart failure. Recent studies suggest that cardiomegaly is associated with a higher risk of sudden cardiac death. Heart failures increase with age, more common in males, and African Americans. According to research conducted in June 2019, half of the people diagnosed with heart failure die within 5 years of being diagnosed. Cardiomyopathy is also associated with cardiomegaly.The causes of cardiomegaly vary from patient to patient, depending on each case. Many times this condition results from high blood pressure (hypertension) or coronary artery disease. An enlarged heart may not pump blood effectively, resulting in congestive heart failure. Cardiomegaly may improve over time, but many people with an enlarged heart (dilated cardiomyopathy) need lifelong treatment with medications. Having an immediate family member who has or had cardiomegaly may indicate that a person is more susceptible to getting this condition (congenital).