Pulmonary regurgitation (PR) is associated with adverse outcomes late after tetralogy of Fallot repair. Accurate assessment of PR in these patients is, therefore, fundamental to their clinical treatment; however, accurate ultrasound markers of severity are as yet poorly defined. This is a prospective study of 34 adult patients with repaired tetralogy of Fallot. Cardiac magnetic resonance imaging was used to assess the PR fraction and its hemodynamic significance on the right ventricular volumes. Regurgitant fractions >/= 20% were associated with significant increases in right ventricular end-diastolic volumes. Echocardiographic continuous wave Doppler profiles of the PR jet were used to calculate pressure half-time. Pulmonary pressure half-time < 100 milliseconds was found to be a good indicator of hemodynamically significant regurgitation. This measure is highly reproducible and easily accessible.