It would be very unusual for a 2 month old guinea pig to die of a heart attack. I would be worried that it was something else instead. Perhaps he was sick when you got him (was he from a pet store?). Maybe you should have your other guinea pig looked at by a vet.
I recommend weighing your guinea pig every week. That way, if it doesn't feel good and doesn't eat as much, you can tell and take it to a vet.
Guinea Lynx :: Weigh Weekly!