 A small vessel diameter, the presence of posterior calcification, occlusion, hematoma, or an earlier placement of a bypass origin, may make access to the vascular system too difficult.Percutaneous transluminal coronary angioplasty (PTCA) is contraindicated in patients with left main coronary artery disease, due to the risk of spasm of the left main coronary artery during the procedure.Also, PTCA is not recommended if there is less than 70% stenosis of the coronary arteries, as the stenosis it is not deemed to be hemodynamically significant below this level.