Ventricular septal defect in cats: interpreting the Doppler
Asymptomatic 4-month-old kitten with a grade 4/6 holosystolic murmur loudest at the right sternal border. Echocardiography shows a 3 mm perimembranous ventricular septal defect just below the aortic valve, with left-to-right flow at 5 m/s. Normal left atrial and ventricular size.
How do you interpret these findings?
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A. It indicates severe pulmonary hypertension
With pulmonary hypertension, right ventricular pressure approaches left ventricular pressure and velocity across the defect falls (or flow reverses). A velocity of 5 m/s rules it out.
B. The high velocity indicates a massive shunt requiring urgent surgical closure
It is the opposite: large (non-restrictive) defects equalise pressures and the flow is slow. Shunt size is judged by left atrial and ventricular dilation, which are normal here.
C. It is a restrictive VSD: the high velocity indicates normal right ventricular pressure and the prognosis is good
Correct. A small defect maintains a large pressure difference between the ventricles (about 100 mmHg, 4 × 5²), indicating normal right ventricular pressure. With normal left chambers, the shunt is small and many cats live without treatment.
D. A grade 4/6 murmur means the defect is large and the prognosis poor
In VSD, murmur intensity does not correlate with size: small defects, with very turbulent flow, often produce louder murmurs than large ones.
lightbulb Key takeaway
VSD is one of the most common congenital heart defects in cats. Severity is defined by shunt size (left chamber dilation, Qp:Qs ratio) and pulmonary pressure, not murmur intensity. Small defect + high velocity + normal chambers = good prognosis. Watch for developing aortic regurgitation.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.