Heart after an angioplasty. Angiography blood vessel X_ray footage showing a radio_opaque contrast medium bright being injected by a catheter right through the left subclavian vein and towards the heart bottom left following an angioplasty. An artery in the heart had been affected by stenosis narrowing and the angioplasty operation had treated this by widening it. Such narrowing typically occurs due to a build_up of atheroma, a cholesterol_rich plaque, on the inside wall of an artery or vein. This is common in patients with high blood pressure. During the procedure, a balloon is introduced into the narrowed area and then inflated, which forces open the blood vessel, permitting normal blood flow. This post_angioplasty test is done to ensure the blood vessel is no longer blocked. The radio_opaque contrast medium allows blood vessels to be seen on an X_ray.