Narrowed coronary arteries. Coronary angiogram (X-ray) of a 59 year old patient with severe stenosis (narrowing) in the left anterior interventricular coronary artery (running down left) and the left circumflex artery (centre). One of the narrowed areas can be seen in the interventricular coronary artery at centre left. The coronary arteries are found on the surface of the heart, and supply blood to the heart muscle. Narrowing of these arteries is usually caused by fatty deposits called atheroma. This can block the arteries and cause a heart attack (myocardial infarction, MI). Treatment is by coronary angioplasty to widen and strengthen the arteries, or a coronary artery bypass operation to graft new arteries on to the heart.