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Chest rheography was used to study central hemodynamics in 134 healthy males aged 18-28 in comfortable weather conditions and discomfortable ones, that is at equivalent-effective temperature 17-24-degrees-C and above 27-30-degrees-C, respectively. In trained subjects from native and nonnative population under comfortable weather conditions heart rate (HR) proved to be significantly reduced as compared to untrained subjects (57.6+/-1.1 and 56.2+/-1.2 against 73.9+/-1.7 and 70.4+/-0.9), whereas stroke volume in trained males was significantly larger (by 14.2 and 14.0 %, respectively). Minute blood volume (MBV), cardiac and stroke indices, systolic and diastolic pressure showed no significant differences. Heat discomfort gave rise to a slow - pulse trend in trained subjects from both native and nonnative populations, in untrained subjects, especially nonnatives heart rate accelerated. MBV increased in trained native and nonnative examinees by 11.0 and 11.1 %, respectively, while in untrained natives the rise reached 17.2 %. This was secured by stroke volume elevation by 14.3, 10.7 and 11.2 %, respectively (p<0.05), in nonnatives by acceleration of heart rate by 11.2 %. A trend to lowering of arterial pressure was more marked in untrained examinees of both populations. It is evident that in conditions of arid zone heat discomfort trained subjects from both native and nonnative populations exhibited adequate hemodynamic responses, whereas strain was observed in circulatory system functioning when it adapted to heat discomfort in untrained nonnatives.