Prevalence and clinical importance of heart murmurs in racehorses

Objective-To determine the prevalence of various types of heart murmurs in Thoroughbred racehorses and assess their association with performance by ec hocardiography and review of the horses' race records for the preceding 2 y ears. Design-Clinical and retrospective study. Animals-846 Thoroughbred racehorses. Procedure-Cardiac auscultations were performed by 3 individuals; for 30 hor ses, Doppler echocardiographic examinations were also performed. Statistica l analyses of race records for 753 horses were performed to assess associat ion of heart murmurs with performance. Results-Heart murmurs were detected by cardiac auscultation in 686 of 846 ( 81.1%) horses. Systolic murmurs over the heart base were most common; 365 ( 43.1%) horses had systolic murmurs that were loudest over the pulmonary val ve area, and 232 (27.4%) horses had systolic murmurs that were loudest over the aortic valve area. Systolic murmurs over the tricuspid valve area were detected in 241 (28.5%) horses, whereas systolic murmurs over the mitral v alve area were detected in only 32 (3.8%) horses. Diastolic murmurs were mu ch less common than systolic murmurs. Review of race records did not reveal a significant association between murmurs and performance. Conclusions and Clinical Relevance-Results suggest that heart murmurs are a common finding in racehorses; most of these heart murmurs do not appear to be clinically important.