A 55-year-old woman with hypertension and hyperlipidaemia presents to her GP with exertional chest tightness relieved by rest. Stress test confirms stable ischaemic heart disease. Her blood pressure is 130/80 mmHg and heart rate 78 bpm. She is on perindopril, atorvastatin and aspirin. Which additional medication provides prognostic benefit in stable angina with prior MI or established coronary artery disease?