Heart murmurs: what matters

Cardiac murmurs are a common finding in the adult horse and the majority are physiological. However, it is necessary to be able to differentiate between variations of normal and abnormal to ensure that potential performance and safety limiting conditions are identified and appropriately evaluated. The most common murmurs vary depending on the predominant horse type and age that is being evaluated. Cardiac examinations, including cardiac auscultation, are a fundamental part of determining the likely diagnosis when a murmur is auscultated, and also form part of the decision-making process to identify what is likely to be significant. Loud (>3/6) and wide-radiating murmurs should undergo further evaluation in horses used for ridden exercise. Differentiation of diastolic from systolic murmurs is extremely important for decision-making. The most common left-sided systolic murmurs are associated with physiological aortic flow, mitral regurgitation, increased pulmonary flow secondary to a ventricular septal defect, and a ‘haemic’ murmur caused by changes in blood viscosity. The most common right-sided systolic murmurs are associated with tricuspid regurgitation and turbulent blood flow through the defect of a ventricular septal defect. Left- and right-sided diastolic murmurs are most commonly associated with aortic regurgitation, although in certain groups short, squeaky diastolic murmurs that are usually intermittent can be physiological in nature.