The purpose of this study was to investigate cardiovascular responses in subjects with paraplegia (P) during prolonged upper body exercise in a hot environment. In addition, the effect of the level of the lesion on cardiovascular regulation of persons with paraplegia was studied. Four P with lesions between T2-T6 (P1), five P with T7-T8 lesions (P2), four P with lesions between T9-T12 (P3), and 10 control subjects (C) performed 45-min arm-cranking exercise at 40% of the individual peak power output, in a climatic room at 35 degrees C with a 70% relative humidity. From the 15th to the 45th min, cardiac output (Q) and oxygen uptake (VO2) remained unaltered in all subjects, except a significant decrease of Q in P1. Stroke volume (SV) decreased significantly in both P (-20%) and C (-18%) during the test. Heart rate (HR) increased in compensation for P2 (56%), P3 (65%), and C (55%), whereas HR in P1 did not increase significantly. Hemoglobin concentration changes, representing total plasma volume changes, increased significantly in P2, P3, and C but not in P1. Weight loss and sweat rate increased relative to the sensate skin area and, thus, to the level of the spinal cord lesion (P < 0.01). In conclusion, P with lesions below T6 are able to maintain a stable Q by increasing HR to compensate for the declining SV during exercise in a hot environment. P with lesions above T6 cannot fully compensate for the reduction in SV by an increase in HR, therefore, Q declines.