Acute ingestion of a low dose of alcohol (0.3 g/Kg) in a group of 18 healthy volunteers does not alter RR mean nor RR variance, producing only a slight decrease in the heart rate variability (HRV) measured by the mean momentary arrhythmia. However, power spectral of the HRV signal shows appreciable changes in the magnitude of the short-term RR fluctuations. Low frequency RR oscillations (0.02-0.06 Hz) increase in power during the 20-45 min. period after alcohol intake, while middle (0.08-0.15 Hz) frequency oscillations decrease in power during the 20-60 min. period and higher (0.20-0.35 Hz) frequency oscillations decrease in power during the 5-60 min. period after intake. The most drastic changes were observed in the middle frequency oscillations during the 20-30 min. period after intake while higher frequency oscillations seem to be less affected by the alcohol ingestion.