Platelets form blood clots when they land on top of irritated, inflamed plaque. Although the platelets are trying to ease the inflammation, they only cause more, which brings even more platelets. These platelets pile up until they fill the entire artery, which will cut the heart off from its blood supply.
Platelets do good work if you nick yourself with a razor. They're nice and calm until they come up against something rough. When they do hit that rough patch, they degranulate and grab on to the lining like it's a life preserver. If the roughness is a cut in the skin, you're glad they arrived on the scene because they're there to make a clot at the end of the blood vessel, which helps you stop bleeding.
But if that rough patch is on the inside of an artery that's been plastered over with cholesterol, then these platelets can pile up until they fill the entire artery. That can cut the heart off from its blood supply. When that happens, you're in a world of trouble.
Why? Blood clots are like party guests. Sometimes they mingle; sometimes they plant in one place and block all the other guests who are trying to get into the kitchen. Sometimes a clot that's been at one party may wander down your arteries looking for a more happening scene. Like stealing your father's car, it's a thrill-seeking romp that could prove deadly. That clot may catch up to another group of party guests in an even smaller space and get completely stuck so your blood can't even get through the door. If those guests are partying in a vital area, all the festivities can be over for good-and in a hurry. That's a heart attack.