A Holter monitorization study was performed in 100 voluntary university students (64 men and 36 women). The mean age was 23.6 years and organic heart disease was ruled out in all cases. Data were analysed in different subgroups including the practice of physical activity and subjects smokers or alcohol consumers. The maximum heart rate (HR) achieved during the wake period was 138.3 +/- 20.43 beat/m. Minimum daytime heart rate was 61.42 +/- 10.32 beat/m and it was below 60 beat/m in 41 subjects. During the nighttime period, the maximum heart rate achieved by the group was 89.34 +/- 11.31 beat/m. Minimum nighttime heart rate was 45.82 +/- 6.35 beat/m. Maximum heart rate in men was 134.3 +/- 21.35 beat/m, while in women was 145.42 +/- 16.36 beat/m. Eighty students presented one or more arrhythmias, among them 28 women and 52 men (p = NS): 92% in sportsmen and women groups as compared with 79% in the non sports practicers, 90% of alcohol consumers and 82% between subjects who smoked and drank, compared with 63% in the non drinkers (p < 0.006). 48% of the subjects presented one or more supraventricular arrhythmias during the daytime or during the nighttime (p = NS). Ventricular rhythm disturbances were found in 20 subjects. There was only one case who had a non sustained ventricular tachycardia of 4 complexes. These disturbances were not increased by practising sport nor by toxic habits. In 15 cases we found sinoatrial block, with a male predominance. Five subjects presented some type of atrioventricular block, 4 of which were alcohol and tobacco consumers.(ABSTRACT TRUNCATED AT 250 WORDS)