The influence of some pulmonary ventilation alterations (the normal ventilation at rest = control), the hyperventilation (HV) lasting 75 s, the hypoxic-hypercapnic ventilation (HXV) lasting 3 and 6 min) on the instantaneous QRS vectors was investigated in 42 young healthy women (19-24 years old). The magnitude and the direction of instantaneous QRS vectors in the 10th to the 70th ms and in QRS max were constructed from the Frank lead ECG. The significant alterations of the direction (angle) were found in the 30th ms and QRS max at HXV and in the 60th ms at HV. A significant decrease in the magnitude of instantaneous vectors was found in the 10th to 50th ms after 6 min of HXV, in the 30th to 50th ms at 3 min of HXV, in the 40th to 50th ms at HV. These alterations were the most marked in the horizontal plane. We suggest that the alterations of the instantaneous QRS vectors were caused by the influence of the autonomic nervous system or humoral agents, but not by heart position, Brody’s effect or lung hyperinflation.