- The purpose of this study was to determine whether resting heart rate variability (HRV) is reproducible with short sampling measurement periods using an office-based personal computer measurement system. Eight healthy active women participated in ECG analyses on 2 days within 1 week under controlled environmental and physiological conditions. After they rested for 10 minutes, a 10-min ECG was recorded. HRV was determined from a 2.5- and 5-min sample period using both time domain variables (meanRR and SDNN) and frequency domain variables (LF, HF, LF:HF). Repeated measures ANOVA found no significant differences between Day 1 and Day 2 for either sampling period (p > or = 0.23). For both the 2.5- and 5-min sampling periods, the intraclass correlations between days for the time domain variables showed good reproducibility (R = 0.86-0.90). The reproducibility of the frequency domain variable was only average (R = 0.67-0.96), with the LF:HF ratio yielding the higher R values.