title: Day to day and beat to beat variation in normal 3 orthogonal lead electrocardiograms.
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003201:Computers; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000502:physiology*; D006801:Humans; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D010507:Periodicity