Sample size estimation: in this high risk population we expect a rate of major and minor bleeding of >5% for the UFH group vs a 3% event rate in the bivalirudin group. Aiming for a 0.05 alpha and 0.80 power, a total of 662 patients will need to be enrolled (331 patients per group). This will be increased by about 25% (leading to a total of 830 patients) because of considerable uncertainty about expected end-point rates.