Platelets are actually fragments of larger cells that are crucial to the formation of clots. clumping (called aggregation) of platelets is the body's most rapid response to stop bleeding from an injured site. however, in some situations the clumping of platelets is not desirable, such as when a plaque in a coronary artery ruptures. in this situation, the rapid clumping of platelets can cause a clot that then completely blocks the coronary artery and results in a heart attack (myocardial infarction). one of the most effective and widely available drugs to prevent the aggregation of platelets is: