Physiological valvular regurgitation in clinically normal young racehorses: prevalence and two-dimensional colour flow Doppler echocardiographic characteristics.

Colour flow Doppler echocardiographic examinations were performed on 15 horses; 10 Thoroughbreds and 5 Standardbreds; 9 mares, 5 geldings and 1 stallion; mean +/- s.d. 3.4 +/- 1.1 years. Cardiac murmurs were audible in 12 horses (80%), but these had characteristics consistent with functional murmurs in all horses. A standardised two-dimensional (2-D) and M-mode echocardiographic examination was unremarkable in all horses except that aortic valve prolapse was identified in 3 horses, tricuspid valve prolapse in 2 horses and mitral valve prolapse was present in one horse. Colour flow Doppler echocardiography revealed laminar antegrade flow in most sites but variance was noted in the right ventricular outflow tract in some horses. Small regurgitant jets associated with the aortic valve were seen in 12 horses (80%), with the tricuspid valve in 7 horses (46%), with the pulmonary valve in 4 horses (26%) and the mitral valve in 4 horses (26%). It was concluded that with colour flow Doppler echocardiography, as in other species, small regurgitant jets could be detected in many normal horses.