The diagnosis of carditis in acute rheumatic fever traditionally depends on characteristic auscultatory findings. The advent of pulsed and colour Doppler echocardiography provides a method of detecting minor degrees of pathological regurgitation without characteristic clinical signs. Using strict criteria, pathological left heart regurgitation can be differentiated from physiological regurgitation: colour Doppler must show a substantial colour jet in two planes extending well beyond the valve leaflets; pulsed Doppler must confirm a high velocity signal, holosystolic for mitral regurgitation, or holodiastolic for aortic regurgitation. Several centres have observed subclinical carditis in children with acute rheumatic fever. We are confident that we are not overdiagnosing valvulitis, having tested this in a blinded fashion. Subclinical valvulitis should be accepted as evidence of carditis, a major diagnostic criterion for acute rheumatic fever.