Here is the difference between a normal heart and an enlarged heart (Cardiomegaly).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.