Respiratory symptoms in tetralogy of Fallot with absent pulmonary valve are believed to be due to bronchial compression secondary to dilated pulmonary arteries; however, not all patients are born compromised. Echocardiographic morphometry of the right-sided structures was investigated to determine the possible relationship between anatomy and clinical presentation. Twenty-five patients were identified, and 15 had preoperative echocardiograms. Patients were divided into two groups: those with respiratory distress (group I, n = 9) and those without (group II, n = 6). No difference was noted in branch pulmonary artery diameters between groups; however, the pulmonary valve/ aortic valve ratio, reflecting the dimension of the narrowest pathway from the right ventricle, was larger in group I (0.74 +/- 0.15 versus 0.60 +/- 0.07, p < 0.05). Pulmonary valve diameter correlated with main and right pulmonary artery diameters. We conclude that patients with tetralogy of Fallot with absent pulmonary valve and respiratory compromise have a greater pulmonary valve/aortic valve ratio but do not have greater dilatation of proximal branch pulmonary arteries. This suggests that the pathophysiology is not due solely to compression of the bronchi but is also related to the blood flow dynamics in the pulmonary vessels.