Postoperative echocardiograms were obtained in conjunction with cardiac catheterization in 14 patients with d-transposition of the great arteries who had undergone the Mustard operation. All 14 patients had atrioventricular valve fluttering demonstrated echographically, although the degree and type of fluttering of both valves varied in each patient. Significant tricuspid valve fluttering was not demonstrated in two patients. Atrioventricular valve fluttering was not related to any one hemodynamic residual. The study suggests that atrioventricular valve fluttering was related to the relatively restrictive atrial tunnel, resulting in turbulent blood flow across these valves. Two patients with d-transposition of the great arteries who underwent repair by the Rastelli operation (without an intra-atrial baffle) did not have atrioventricular valve fluttering.