Based on my experience, "J B" and "Tracy M" gave you good answers.
In May I had a heart attack
. After that my EF was about 33%. Later in May I had triple bypass surgery
. After the surgery but before I got out of the hostpital my EF was 40%. After I got out of the hospital I recuperated for one month, taking some walks when weather permitted, then I went into an exercise program ("phase II" rehabilitation
) exercising three times a week for 12 weeks. After that my EF was up to 50%.
Of course, nothing that I have done has "cured" my coronary artery
disease. I still have narrowed arteries in my heart and it is entirely possible I will have another heart attack in the future. By following a much better diet, taking my medications and continuing to exercise I have a good chance of postponing that event for quite a few years and, if I do have another heart attack, surviving it.