The ratio of peak pressure in the right ventricle to that in the left ventricle (PRV/LV) in the operating room thirty minutes after repair of tetralogy of Fallot by an atrial approach, with or without a concomitant transatrial approach, was 0.58 +/- 0.217. It was 0.52 +/- 0.158 when repair was through a right ventricular approach (p for difference = 0.16). This ratio 18 to 24 hours postoperatively was 0.49 +/- 0.148 and 0.45 +/- 0.121 for the right atrial and right ventricular approaches, respectively. The reduction in PRV/LV between the two observations was -0.09 +/- 0.147 for the right atrial and -0.07 +/- 0.110 for the right ventricular approach (p for difference = 0.4). Therefore, the predictive rules for placing a transannular patch, rules derived from patients in whom the right ventricular approach was used and depending in part on the fall in PRV/LV during the first 24 hours after operation, are also applicable to patients in whom an atrial approach, with or without a transpulmonary approach, is used.