Enlarged heart. Coloured chest X-ray of a female patient with gross (severe) enlargement of her heart (red). This is known as cardiomegaly. Here, the severity of the condition has caused the heart to start to fail. There are a variety of disorders that can cause enlargement of the heart, including a weakening of the heart muscle (cardiomyopathy), an infection with a virus, or an enlargement as a response to excessive strain, such as in obesity. The gradual loss of heart function (heart failure) causes breathlessness and exhaustion, even when at rest. Various drugs help in managing the symptoms, with transplantation as a last resort.