Heart attack. Computer composite artwork depicting a heart attack (myocardial infarction), showing an angiogram of coronary arteries and ECG heart traces. Two green ECG (electrocardiogram) traces reveal the electrical activity of a healthy heart- beat (at top) and the irregular heartbeat during a heart attack (at bottom). In the background is a coloured angiogram (X-ray) of the heart (yellow) with coronary arteries (black) on its surface. Coronary arteries supply the heart muscle with oxygen. Blockage of one of these coronary arteries by a clot or narrowed artery walls in atheroscle- rosis starves the heart muscle of blood and is a typical cause of heart attack.