Cause of heart murmurs in 57 apparently healthy cats

Heart murmurs are caused by turbulent blood flow or by vibration of cardiac structures. Turbulent blood flow may originate from structural heart disease or from physiological phenomena. The aims of this study were to establish the cause of heart murmurs in apparently healthy adult cats and to determine whether a heart murmur is a reliable indicator of heart disease. In this retrospective study, we reviewed the medical records of cats in which a heart murmur was detected during physical examination by one of the authors in the period January 2008 to December 2009. Cats younger than 6 months and those with systemic disease were excluded. Timing, grade, and point of maximum intensity of the murmur were determined by one observer (MD) before 2D-, M-mode and Doppler echocardiography. Fifty-seven cats (median age 76 months, range 6-194) were included, 30 neutered females and 27 neutered males. All murmurs were systolic and varied in intensity from 2/6 to 5/6. The point of maximum intensity was the left or right parasternal region in 34/57 (61%) of murmurs. Murmurs were caused by dynamic left ventricular outflow tract obstruction in 25/57 (44%) cats, dynamic right ventricular outflow tract obstruction in 9/57 (16%) cats, and combined dynamic left and right outflow tract obstruction in 11/57 (19%) cats. In 5 (9%) cats the cause of the murmur could not be identified. Heart disease was present in 50 (88%) cats, namely, left ventricular hypertrophy in 44 (77%) and congenital defects in 6 (11%) cats. In conclusion, most heart murmurs in apparently healthy cats are detected in the left or right parasternal region and are caused by dynamic left and right ventricular outflow tract obstruction. Because most cats (88%) with a heart murmur had heart disease in this study, if a heart murmur is detected in an apparently healthy cat, echocardiography is recommended to determine the cause of the heart murmur and the presence of heart disease.