Feline cardiac murmurs are frequently encountered in clinical practice and may be inducible (secondary to stress, pain, or fear) or noninducible (continually present independent of external stimuli). Previous studies have shown that a high percentage of cats with murmurs (particularly inducible murmurs) lack evidence of structural heart disease. In this prospective study, 32 clinically healthy cats with heart murmurs but no other comorbidities were evaluated at a cardiology specialty center between March 24, 2005, and January 25, 2007. Physical and echocardiographic examinations were conducted on all cats. Doppler blood pressure measurements were conducted in 15 of 32 cats, including 11 of 17 cats subsequently found to have cardiac disease. Mean systolic blood pressure measured less than 180 mm Hg in all cats. Normal echocardiographic studies with no evidence of cardiac disease were reported in 15 of 32 cats (47%). The  cause of the physiologic murmur was identified as dynamic right ventricular outflow tract obstruction (DRVOTO) in 2 of 15 cats, dynamic left ventricular outflow tract obstruction (DLVOTO) in 2 of 15 cats, and DRVOTO with DLVOTO in 1 of 15 cats. In 10 of 15 healthy cats, the cause of the murmur could not be determined. Echocardiographic evidence of cardiac disease was identified in 17 of 32 cats (53%). Twelve of 17 cats with heart disease were found to have left ventricular concentric hypertrophy. This was accompanied by papillary muscle enlargement in 6 of 12 cats, focal endomyocardial thickening in 3 of 12 cats, DLVOTO in 5 of 12 cats, systolic anterior motion of the mitral valve in 3 of 12 cats, and mild left atrial enlargement in 1 of 12 cats. Murmur etiology was identified in 11 of 17 cats with echocardiographic evidence of cardiac disease. This included elevated aortic velocities and DLVOTO in 5 of 11 cats; DRVOTO in 2 of 11 cats; elevated aortic velocities in 2 of 11 cats; mitral valve disease in 1 of 11 cats; and mitral valve disease, DRVOTO, and DLVOTO in 1 of 11 cats. Murmur etiology could not be identified in 6 of 17 cats with echocardiographic evidence of heart disease. The fact that > 50% of apparently healthy cats in this study had structural heart disease strongly suggests that feline heart murmurs found on routine examinations warrant further investigation.

Commentary: The high prevalence of occult cardiac disease in this population should impel veterinarians to recommend further cardiologic evaluation in feline patients with heart murmurs. It is hard to know if results from this small study would remain robust with a bigger sample size. Future investigations should examine larger and more diverse feline pet populations to see how well the current findings can be generalized.—Indu Mani, DVM, DSc

Prevalence of echocardiographic evidence of cardiac disease in apparently healthy cats with murmurs. Nakamura RK, Rishniw M, King MK, Sammarco CD. J FELINE MED SURG 13:266-271, 2011.