Studies in young adults show that a greater proportion of heat is gained shortly following the start of exercise and that temporal changes in whole-body heat loss during intermittent exercise have a pronounced effect on body heat storage. The consequences of short duration intermittent exercise on heat storage with aging are unclear. We compared evaporative heat loss (HE) and changes in body heat content (Hb) between young (20-30 years), middle-age (40-45 years) and older males (60-70 years) of similar body mass and surface area, during successive exercise (4x15-min) and recovery periods (4x15-min) at a fixed rate of heat production (400W) and under fixed environmental conditions (35°C/20% relative humidity). HE was lower in older males versus young males during each exercise (Ex1: 283±10 vs. 332±11 kJ, Ex2: 334±10 vs. 379±5 kJ, Ex3: 347±11 vs. 392±5 kJ, Ex4: 347±10 vs. 387±5 kJ, all P<0.02), whereas HE in middle-age males was intermediate to that measured in young and older adults (Ex1: 314±13, Ex2: 355±13, Ex3:371±13, Ex4:365±8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2-hours was a greater Hb in older (267±33 kJ, P=0.016) and middle-age adults (245±16 kJ, P=0.073) relative to younger counterparts (164±20 kJ). As a result of a reduced capacity to dissipate heat during exercise, which was not compensated by a sufficiently greater rate of heat loss during recovery, both older and middle-age males had a progressively greater rate of heat storage in comparison to young males over 2-hours of intermittent exercise.