Many patients with congenital heart disease now undergo cardiac surgery based solely on clinical and echocardiographic findings, but those with intracardiac shunts still frequently require cardiac catheterisation because there is no reliable non-invasive method of measuring the pulmonary artery pressure. Blinded to the haemodynamic results two independent observers retrospectively studied the cross sectional echocardiograms of 59 patients with uncomplicated ventricular septal defect to assess whether diastolic backward bowing of the pulmonary valve leaflets towards the right ventricular outflow tract (pulmonary valve prolapse) was associated with pulmonary hypertension. There was considerable interobserver variation in the diagnosis of pulmonary valve prolapse, but concordance was achieved in 27 cases. Mean pulmonary artery systolic and mean and diastolic pressures and the ratios of aortic to pulmonary artery mean pressures were all significantly higher for the group with pulmonary valve prolapse diagnosed by both observers than for the group without, thus showing an association between pulmonary valve prolapse and pulmonary hypertension. Further studies are warranted to determine the usefulness of this cross sectional echocardiographic sign in routine clinical practice.