I am sorry to hear of your cardiac problems however please sit down with your Dr. or one of the Cardiac Nurses to learn all you can re your dx and treatment.
Each person is unique to their own disease and your biggest life change will be to stop smoking.
Fatigue is a distinct characteristic of cardiovascular disease in women; in one study of 515 female heart attack survivors, 70 percent reported unusual fatigue in the weeks before their attacks. If you have heart disease you heart is not pumping effectively and therefore your body is not getting the oxygen it needs = fatigue.
Do stay in touch with your Dr.