An enlarged heart (cardiomegaly) is an increase in the size of the heart. It is not strictly a disease, it is a sign that another health condition is affecting your heart. Some conditions – such as pregnancy – increase demand on the heart. Other conditions can thicken the heart wall muscle or stretch out the heart chambers (dilate) which makes the heart larger. In some people, an enlarged heart causes no signs or symptoms. Others may experience shortness of breath, abnormal heart rhythm or swelling in the legs.