title: Younger at heart: a study of the P-R interval.
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging; D002648:Child; D002675:Child, Preschool; D004035:Diet Therapy; D004562:Electrocardiography; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D010507:Periodicity