I have to have an echocardiogram on Monday...see details?

I have had 2 heart attacks in the past. I have an Internal Cardiac Defribrillator that has never fired. I am tired a lot and can't walk far at all w/out needing to sit, I have to use one of those electric carts in the grocery store. The Doctor thinks my heart may not be pumping a sufficient amount of blood. Can anyone clarify? What's the prognosis if that's the case? I am only 34.