In an enclosed group of tammar wallabies the behaviour of all individuals and the heart rate (HR) of three males were recorded simultaneously. The social structure was characterized by the dominance relationships between the males and the sexual preference of all males for the oldest female. During non-oestrus, dominance was obvious when a male intervened terminating the sexual behaviour of a subdominant one. The relatively low amount of agonistic behaviour between the males is assumed to be due to the clear dominance relationships. Locomotion as well as sexual and agonistic behaviour were accompanied by an acceleration of HR. The HR pattern depended on the intensity of the behaviour, its duration and the animal's identity. Commonly performed sexual behaviour and approach/retreat encounters gave rise to HR values not different from HR values during locomotor activity without interactive components. Social events that occurred infrequently—like fights, and the mating of an oestrous female—were accompanied by strong accelerations of HR indicating high cardiac effort. The mild cardiac activity during common social encounters is consistent with a strategy of maximizing energy conservation. HR patterns during specific behaviour could not entirely be accounted for by the energetic costs of activity. Spreading the forelimbs in response to specific stimuli—like the fly-over of raptors—was indicative of a strong HR response even if the animal was motionless. During specific social encounters like the sexual behaviour of the alpha-male following an intervention—HR responses revealed that arousal might exceed motor activity in affecting HR. Individual differences of these HR responses are attributed to the age, experience and social status of a male.