Heart rate is a convenient and sensitive indicator of emotional tension. It has been shown that in groups of macaques and baboons in which hierarchy has always existed the leader has the lowest heart rate. That fact reflects absence of emotional tension and is noticed when hierarchy is not violated. Heart rates of submissive monkeys are always somewhat higher than the usual basal rate, which indicates that a certain emotional tension exists in them. When monkeys are regrouped there appears a new leader instead of the expelled one. Now the new leader shows the lowest heart rate.