We know that heart attack or in other words damage to the heart due to reduced blood supply is caused due to blockage in the heart's blood vessels. If a major blood vessel is blocked leading to reduced blood supply and damage in a large area of the heart, then this is said to be a major attack. This is mostly life threatening.
Similarly, If a small blood vessel is blocked leading to reduced blood supply and damage in a small area of the heart, then this is said to be a minor attack. This is mostly not life threatening. But yes, it does make the heart weak in most of the cases.