A 3-month-old baby has a 3/6 degree whistling murmur that is high-pitched and broad. Echocardiography shows perimembranic VSD (ventricular septal defect) beneath the tricuspid valve (2 mm in diameter). There is no strain on the heart. A defect of this size need usually not be repaired. Note the high pitches in the frequency distribution; the pressure gradient between the ventricles is 70 mmHg, calculated from the flow.