CoQ10 therapy improves cardiac function only when CoQ10 levels of the heart are low. There is little benefit if you already have high levels of this enzyme. If you have heart problems or a family history of heart problems, deciding whether or not to take CoQ10 is rather easy. I say emphatically, "yes!"
In one study 91% of the patients showed improvement within 30 days of taking CoQ10. I've been to lectures by a preeminent cardiologist from the New England Heart Center and he personally takes 180 mg daily as a heart protective dose. For serious heart problems he gradually builds his patients up to 300-400 mg daily.
But the questions still remains, "if I don't have heart problems, do I need it?" As we age, there is a higher probability of having low levels of CoQ10. I would recommend for preventive maintenance taking 60-100 mg daily for someone without a specific problem.
CoQ10 has also been shown to be of considerable benefit in the treatment of hypertension and other cardiovascular diseases. Of course, there are other great supplements for the heart that can protect you such as vitamin E, natural beta-carotene, vitamin C due to its effect on lipoprotein(a), L-carnitine, magnesium, B-6, folic acid, niacin, lecithin, calcium and magnesium in proper ratios, herbs like hawthorne berry or cayenne and the good omega oils.
You can read all about these in my book, Aging Without Growing Old.