Enlarged heart. Coloured chest X-rays of a right side-view (left) and a left side-view (right) of a patient with an enlarged left ventricle of the heart (white mass at centre of images). The patient has taken a barium meal to highlight the oesophagus (behind heart). The enlargement of the heart is caused by mitral valve insufficiency. The mitral valve is between the heart's left atrium (upper chamber) and left ventricle (lower chamber) and prevents the backflow of blood. When the valve is not working properly the heart has to pump harder to get blood around the body. As the heart is a muscle, it grows if it has an increased workload.