Allopurinol is a drug commonly used to treat gout. However recent studies have shown it has the potential to help improve oxygen supply to heart muscle. In this study the Investigators aim to find out if allopurinol slows down the onset of angina symptoms, as seen by a doctor on a tracing of the heart (ECG- electrocardiogram), for patients who have been diagnosed with heart disease, when exercising on a treadmill. The Investigators are also are trying to figure out the best dose of allopurinol to use and to see how quickly it begins working. To do this the investigators will recruit patients with angina, exercise them on a treadmill after giving different doses of allopurinol and see if there is an improvement in their time to bring on angina symptoms and signs. Patients recruited to this trial will receive three different treatment regimes over a six week period. Each treatment regime will last for one week with a one week rest period between each regime. This will involve up to eleven visits to Ninewells Medical School, Dundee for testing.