The mitral valve (between the leaft atrium and ventricle) is most commonly affected, although 25 per cent of people with RHD have mitral and aortic valve involvement. Valves in the right side of the heart are only rarely involved. As the aotic valve becomes increasingly dysfunctional, the left atrium becomes progressively dilated and atrial fibrillation (AF) develops. The combination of stagnation of flow and AF may generate thrombosis, leading to strokes. It also causes increasing pressure in the pulmonary circulation and ventricular hypertrophy that eventually leads to heart failure.