In 27 (18%) of the 151 patients who underwent transatrial closure of isolated ventricular septal defect (VSD) between 1966 and 1979, the tricuspid valve was partially detached in order to achieve better exposure. All 27 patients had defects of the membranous or paramembranous type situated behind the tricuspid septal cases, tight chordae tendineae crossed over the defect and inserted in the edge of the VSD. A 15 to 20 mm incision in the septal leaflet was usually needed to expose the defect sufficiently. There were two operative deaths among the 27 patients, both unrelated to the tricuspid incision. The remaining patients had uncomplicated postoperative courses. There were no long-term complications or instances of significant tricuspid valve incompetence, major residual shunt, or heart block at follow-up. Three patients, operated upon at the ages of 3, 3, and 6 years, respectively, had residual pulmonary hypertension. In one patient, who died 4 years postoperatively in a traffic accident, the tricuspid valve was intact and the previous incision could hardly be seen. It is concluded that detachment of the septal tricuspid leaflet is a safe procedure during transatrial closure of a VSD.