Renal failure & Steroids (prednisolone) predispose people to blocks in the tubes supplying blood to the heart. So does hypertension. If your treadmill is strongly positive you Should undergo an angiogram. However if you have walked for more than three stages (of Bruce protocol: >9 mins) without marked ECG changes you probably can be managed by medications which will involve intense cholesterol lowering (LDL<70 mg%) and asprin. Sometimes there is thickening of the heart muscle due to high blood pressure (easily seen on an echocardiogram) which may make your stress ECG test falsely positive. So the other way to check if there is a significant block in a major artery is a stress test: If a large area is suffering from decreased supply you will need an angiogram, if there are small areas you can be managed medically. Definitely keeping your bad cholesterol very low is much more important than CoQ. There are no large randomised studies with CoQ although its mechanism of action as an antioxidant seems conceptually very encouraging; but till now no antioxidant has been unequivocally shown to help and many like VitE have fallen by the way side. A better proposition is taking lot of fresh fruits, vegetables and fibre after consulting your nephrologist.