A retrospective study of 10 horses with bacterial endocarditis was performed in order to describe the echocardiographic findings in horses with bacterial endocarditis, in conjunction with clinical signs and post mortem findings, and to evaluate the usefulness and the formulation of a prognosis. Echocardiographic and post mortem examinations were performed in 7 horses. Post mortem examination alone was performed in 2 horses and echocardiographic examination alone performed in one horse. No breed or sex predilection was obvious. Mean age +/- s.d. was 2.12 +/- 3.32 years. Predominant clinical signs and abnormal clinical pathology data were fever, cardiac murmur, tachycardia, tachypnoea, hyperfibrinogenaemia, anaemia and leucocytosis. Pasteurella/Actinobacillus spp. and Streptococcus spp. were most commonly cultured. Vegetative lesions were found most frequently on the mitral valve and secondarily on the aortic valve. The location and number of lesions identified with echocardiography in the horses accurately described the lesions found on post mortem examination. Medical treatment was attempted in 50% of the horses. Serial echocardiography was used to assess the response to treatment in 2 horses. All horses with vegetative lesions of the mitral and/or aortic valve died or were subjected to euthanasia due to the severity of their cardiac disease. Both horses with tricuspid valve endocarditis were cured of the infection, one horse returned to racing after antimicrobial therapy and the other was subjected to euthanasia due to severe laminitis.