If you're talking about a mutation that will increase the reproductive success of your children(or more likely grandchildren in the case of reduced chance of a

If you're talking about a mutation that will increase the reproductive success of your children(or more likely grandchildren in the case of reduced chance of a heart attack), then the advantage would have to be even greater because of the high chance that your descendants don't have the same mutation. I'm not saying there's no natural selection occurring, but that saying that heart disease is the #2 killer of Americans out of context likely overstates the selection pressure heart disease causes.