A heart attack occurs when an area of the heart is cut off from blood to the point where it can no longer survive (often due to atherosclerosis). This is called myocardial infarction. A heart attack, though, is not necessarily fatal (over 50% of heart attack victims live for at least a year past the attack) because the surrounding heart muscle continues to work, giving time for a scar to form over the dead muscle and allow the heart to regain functionality. The outlook for a heart attack victim depends greatly on the area and size of the muscle which is affected and the manner with which it was affected:Cardiac Arrest
In some cases a severe blockage of one of the coronary arteries stops the heart muscle's contractions all together or causes one of the ventricles to contract randomly (known as ventricular fibrillation). Both of these conditions are known as cardiac arrest.Coronary Spasm
In some rare cases the coronary arteries can go into what is called a spasm, cutting off blood supple to large areas of the heart long enough to stop it from functioning. Scientists to not yet understand why these spasms take place.Heart Block
If some of the Purkinje fibers of the heart are damaged as a result of blood deficiency, the condition known as heart block may result. When part of the electrical conducting system is damaged the action potentials from the S-A or A-V nodes fails to reach affected region of the heart muscle and it's cardiomyocytes do not contract in rhythm with the rest of the heart.
Most coronary blockages are treated with the coronary bypass surgery.
A new alternative to surgery is the treatment with an enzyme streptokinase. When streptokinase is introduced into the arteries clotting can be reopened in almost 80% of the cases and expensive surgery is no longer required.