They Say I Have Half Heart And Its At 30

They say I have half heart and its at 30 percent. 9 yrs ago I had triple bi-pass and the doctor say two of them are blocked and one is open. says heart is dead on one side but why am I having pain the same pain that sent me to the heart doctors before with two heart attacks and a massive heart attack which lead to the triple bi-pass? If the pain is a sign that I have a blockage does that mean that some of it is still alive?