We studied the time- and frequency-domain indexes of heart rate variability (HRV) in 653 patients without any evidence of heart disease relative to age, gender, heart rate, body mass index, and functional capacity. There was an inverse correlation of HRV with heart rate (p <0.001). HRV indexes decreased with increasing age, differed by gender, and were higher in patients with higher functional capacity. No correlation was noted between HRV and body mass index.