title: Heart rate variability: back to the beginning.
authors.forename: Tomas
authors.initials: T
authors.lastname: Kara
authors.forename: Jiri
authors.initials: J
authors.lastname: Nykodym
authors.forename: Virend K
authors.initials: VK
authors.lastname: Somers
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D001341:Autonomic Nervous System / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006321:Heart / Q000294:innervation* / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012737:Sex Factors; D013223:Statistics as Topic; D014630:Vagus Nerve / Q000502:physiology