Arterial embolism. Coloured angiogram (X-ray) showing an embolus blocking the left subclavian artery (red, upper centre) in the arm. Blood only flows part of the way into the arm as the embolus has become trapped in the artery, stopping blood flow beside the humerus (upper-arm bone, blue) at lower right. The bones of the shoulder (upper frame), ribcage (blue, centre left) and spine (red, down left) are also seen. An embolus may be a blood clot, a clump of bacteria, a piece of fat, a gas bubble or a tumour. Symptoms may include pain and, without drug or surgical treatment to remove the embolus, tissue death. In an angiogram, an X-ray opaque dye is injected into an artery.