Segments of resting heart rate were submitted to spectral analysis in order to assess changes in spectral power with age. Different frequencies of heart rate variability have been related to vagal and sympathetic cardiac control. Data were from 56 male volunteers ranging in age between 18 and 65 years of age. Spectral results revealed that respiratory sinus arrhythmia declined less with age than lower (vasomotor) frequencies. Assessment of total (rather than relative) power at respiratory frequencies revealed the expected drop in power with age. Thus, the decline in heart rate variability with age may not be due predominantly to a decline in frequencies related to respiration.