Pacemaker in heart disease. Coloured chest X-ray showing a pacemaker (right) fitted to a 73-year-old male patient with an enlarged heart (cardiomegaly) atrial fibrillation, ischaemic heart disease and chronic obstructive pulmonary disease (COPD). A pacemaker supplies electrical impulses to the heart to maintain the heartbeat at a regular rate. It may be external (worn on a belt) or internal (implanted in the chest, as here).