To evaluate the possibly confounding effects of age, gender, heart rate, tobacco and alcohol ingestion on the coefficient of variation of the electrocardiographic R-R interval (CVRR), ECGs in the supine posture were obtained in 68 healthy men and 33 healthy women. The C-CVRSA and C-CVMWSA (two component CVs reflecting respiratory sinus arrhythmia and Mayer wave related sinus arrhythmia, respectively) were computed in each subject from component spectral powers using autoregressive spectral and component analyses. Results of multiple regression analysis indicated that age was inversely related to CVRR, C-CVRSA and C-CVMWSA in both sexes. Heart rate was positively related to C-CVMWSA in males. However, no significant difference in the CVRR, C-CVRSA or C-CVMWSA was found between males and females. The C-CVMWSA was not correlated with the C-CVRSA in either males or females. These data indicate that the CVRR, C-CVRSA and C-CVMWSA are affected by age and partly by heart rate; gender, moderate smoking or drinking habits might not strongly influence autonomic nervous system function. On the other hand, the C-CVRSA in the supine posture appears to be independent of the C-CVMWSA. The positive relationship observed between the C-CVMWSA and heart rate suggests that the C-CVMWSA may be associated with sympathetic activity.