This study assessed the validity of cine magnetic resonance imaging (MRI) for measuring right and left ventricular volumes by using Simpson's rule in children with complex congenital heart disease. Forty-five patients with complex congenital heart disease (average age 2.6 years) and 10 controls (average age 2.3 years) were evaluated. The whole heart was encompassed by contiguous transverse sections. Ventricular volumes were calculated by adding luminal areas determined in each section at end diastole and end systole. End-diastolic and end-systolic volumes by MRI in both groups correlated well with those by ventriculography (r>0.89). Comparison of the ejection fraction in both ventricles in both groups yielded a good correlation between MRI and ventriculography (r>0.67). MRI technique in both groups had low intraobserver and interobserver variation (<6%). Cine MRI provides a suitable noninvasive means of quantifying ventricular volume in children with complex congenital heart disease.