Chest X-ray of a child with cardiomyopathy (heart failure), showing enlargement of the left ventricle of the heart. The ribs surround the lungs. The diseased heart (centre) is highly enlarged at centre right, due to its swollen left ventricle protruding into this region. Cardiomyopathy is a disease of the heart muscle that makes the heart less efficient at pumping blood to the lungs and the rest of the body. It may be inherited, due to metabolic abnormality, infection or an unknown cause. For an X-ray of this chest after a heart transplant see image M560/267.