Angiography of the chest of a 75_year_old heart failure patient wearing a pacemaker/defibrillator. Angiography is an X_ray examination of the circulatory system, in which a radio_opaque contrast medium is injected into blood vessels to show blood flow. In this clip the medium appears dark, and the flow of blood through the brachiocephalic veins upper left and right and the vena cava down centre to the heart is seen. This is being performed to ensure the veins?condition is good enough to permit the changing of the pacemaker/defibrillator at right. The pacemaker supplies electrical signals to the heart muscle to ensure a steady beat. The device also contains a defibrillator, which shocks the heart back to a steady beat if it starts beating erratically fibrillation.