It makes your blood thinner but it doesn't prevent you. It can be one of the medications that you get after a heart attack but you get also a million other pills. It depends on where your heart is injured. And there are a many other pills that can prevent this.
Taking too much aspirin is bad for you health. You can find it in the group of the acetylsalicylacids. It can give you stomachulcera. It's also dangerous during pregnancy. You are not allowed to take aspirin a couple of days before surgery.