To investigate changes in physiologic and metabolic functions from exercise under acute low-inspired oxygen condition. Thirty three male-football players progressively exercised at submaximal workloads of 60, 90, 120 and 150 watts on cycle ergometer under two randomized conditions of normobaric-hypoxia (15% O2, HYP) and normoxia (21% O2, NOR). Exercise performance, cardiorespiratory and metabolic profiles were continuously monitored. No significant differences between groups on cardiac variables, with the exception of significantly higher heart rate (HR) in HYP at all workloads. Respiratory variables, after 90 watts, showed remarkable increased in HYP (p<0.05). At highest intensity, HYP condition showed significantly reductions of end diastolic volume (EDV), end systolic volume (ESV) and ejection fraction (EF) with significantly higher respiratory rate (RR), tidal volume (VT), pulmonary ventilation (VE) and carbon dioxide production (VCO2) (p<0.05). Exercise under hypoxic condition limits cardiac function but not for respiratory system. The parallel rising in VO2 and VCO2 at higher submaximal workload reflects to the limitation in VO2 with further increasing in VCO2 at maximal intensity. These will reduce physical performance. Awareness of cardiac deteriorations should be concerned for those who have to work hard under low O2 conditions.