An enlarged heart is medically known as cardiomegaly. Cardiomegaly can be caused by a number of different conditions, including diseases of the heart muscle or heart valves, high blood pressure, arrhythmias, and pulmonary hypertension. Cardiomegaly can also sometimes accompany longstanding anemia and thyroid diseases, among other conditions. Infiltrative diseases of the heart, for example, in which abnormal proteins (amyloidosis) or excess iron (hemochromatosis) accumulate within the tissues of the heart, can also cause an enlargement of the heart. Infections, nutritional deficiencies, toxins (such as alcohol or drugs), and some medications have been associated with cardiomegaly. In some situations (for example, pregnancy), there can be a temporary increased demand on the heart, resulting in some temporary enlargement. It is important to remember that an enlarged heart is not a disease itself but a physical sign that can accompany many diseases and conditions. Not all of the associated conditions listed below, however, will always result in cardiomegaly. Treatment and prognosis are dependent upon the underlying cause. A pericardial effusion is the accumulation of fluid in the sac surrounding the heart, which can lead to the appearance of an enlarged heart. Cardiomyopathy is a related term that refers to damage to the heart muscle. Cardiomyopathies are often accompanied by cardiomegaly.