This study is a reexamination of the possibility that exposure to extremely low frequency alternating magnetic field (ELF-MF) may influence heart rate (HR) or its variability (HRV) in humans. In a wooden room (cube with 2.7-m sides) surrounded with wire, three series of experiments were performed on 50 healthy volunteers, who were exposed to MFs at frequencies ranging from 50 to 1000 Hz and with flux densities ranging from 20 to 100 microT for periods ranging from 2 min to 12 h. In each experiment, six indices of HR/HRV were calculated from the RR intervals (RRIs): average RRI, standard deviation of RRIs, power spectral components in three frequency ranges (pVLF, pLF and pHF), and the ratio of pLF to pHF. Statistical analyses of results revealed no significant effect of ELF-MFs in any of the experiments, and suggested that the ELF-MF to which humans are exposed in their daily lives has no acute influence on the activity of the cardiovascular autonomic nervous system (ANS) that modulates the heart rate.