The purpose of this study was to describe the effects of gender and age on heart rate variability (HRV) in healthy volunteers (n = 111; 40 men and 71 women) and in persons after sudden cardiac arrest (SCA) (n = 95; 79 men and 16 women). Frequency-domain measurements and six time-domain measurements of HRV (SDANN, 24-hour SD, SD, RMSSD, RR50, and %RR50) were taken. Two-factor analysis of variance was performed. In general, HRV was significantly lower in healthy women compared with healthy men in all the time-domain and frequency-domain variables except for the high-frequency components, RMSSD, RR50, and %RR50. There were no significant gender differences in the SCA sample. All the time-domain and frequency-domain measurements decreased with age in the healthy sample, but only the frequency-domain measurements decreased with age in the SCA sample.