How high does your heart rate need to be to have a heart attack?

Not related: Your heart rate doesn't have to be high at all to have a heart attack. That's not what causes a heart attack. Blockages in the arteries do. Of course, your heart rate may increase during and after the heart attack but its not the cause.

No simple answer: If your arteries have no blockage, then there is no heart rate that will cause a heart attack. The more blocked the arteries, the lower the hr needed to outstrip the blood supply. There are other factors too, like presence/absence of anemia, hypertension, left ventricular hypertrophy, (wall thickening), and contractility which determine how much blood the heart is using and needs.