What is a Heart Attack?

Figure A shows a heart with dead heart muscle caused by a heart attack. Figure B is a cross-section of a coronary artery with plaque buildup and a blood clot.  

A nice image from the National Heart Lung and Blood Institute of what a heart attack  is.  This represents a rather large heart  attack because of insufficient blood from the LAD or the widow maker. This type of a heart attack would  typically cause changes in the EKG. This would create a STEMI or ST segment Elevated Myocardial Infarction. This means likelyhood is a heart attack involving the full thickness of the heart wall. When this occurs we usually note changes in the EKG.

See   Medical terms you should know for a description of the EKG changes that occur with this type of a heart attack.