This study evaluated heart rate variability and its changes in 30 patients before and after transcatheter closure of secundum atrial septal defects. Heart rate variability data from 30 healthy volunteers with normal echocardiographic parameters and no history of atrial septal defects were included as controls. Values for the SD of all the normal RR intervals (SDNN), the SD of the means of all the 5-min segment normal RR intervals (SDANN), and the mean of all the 5-min SDs of normal RR intervals during the 24-h period (SDNN index) in patients with atrial septal defects before transcatheter closure were statistically significantly different from controls. At 6 months after closure of the defects these values were not statistically different from controls. It is concluded that transcatheter closure of secundum atrial septal defects had positive effects on heart rate variability and, consequently, may contribute to less mortality and morbidity.