In several human adults, certain solar activity rhythms may influence
an about 7-day rhythm in heart rate. When no about-weekly feature was
found in the rate of change in sunspot area, a measure of solar activi
ty, the double amplitude of a circadian heart rate rhythm, approximate
d by the fit of a 7-day cosine curve, was lower, as was heart rate its
elf. The changing time structure (chronome) of heart rate corresponds
to about-weekly features in solar activity and/or relates to a sunspot
cycle.