In order to determine the effect of interatrial baffle repair for transposition of the great arteries(TGA) on sinus node function, we compared percent sinus node recovery times(%SNRT) in 44 TGA pts, 16 before and 28 one year after operation(op). Ten pts had Mustard(M) repair and 18 had Senning's(S) op. The 16 preop pts served as controls. Results are shown as mean %SNRT, ±SD (n) (*p< 0.05 compared to control).The postop mean %SNRT were slightly longer than preop and no significant differences between M and S groups occurred. Six of 10 M pts and 9 of 18 S pts had prolonged %SNRT (> 2 SD above mean pre-op)at one or more CL. One pt from each group had sick sinus syndrome and prolonged %SNRT (236%, 244%, p< 0.05).These data indicate that there is no advantage of one operation over the other regarding alterations in sinus node function. A significantly prolonged %SNRT may identify those at risk for developing serious arrhythmia.