Explain how a blood clot can cause a heart attack?

A blood clot or thrombus is formed pathologically in the blood stream when the clotting cascade is activated inappropriately. This commonly occurs over the rough vessel surface during atherosclerosis of an artery. Platelets, which are cell fragments in blood, stick to the site of AS and cause prothrombin to be converted into thrombin via the action of thromboplastin. Thrombin causes soluble fibrinogen to become insoluble fibrinogen which forms strands, trapping RBCs. If this clot breaks off in a coronary artery it can travel through the aretery and become lodged within the artery, occlusion for blood flow to the heart muscle further down. This causes the muscle to be unable to respire aerobically and as glucose cannot be provided for anaerobic respiration, the muscle starts to die (myocardial infaraction). Heart can't pump effectively hence the risk of death.