Among the more perplexing observations to emerge from recent studies on the biological effects of electromagnetic fields (EMFs) is their ability to sometimes—but not always—blunt heart-rate variability (SN: 1/10/98, p. 29: http://new.sciencenews.org/sn_arc98/1_10_98/bob1.htm). A reanalysis of seven studies on people exposed to EMFs now suggests that a person must be aroused or stressed for EMFs to dampen heart-rate variability.