In 77 young healthy volunteers of both sexes the dependence of the QT interval of ECG on the heart rate was investigated during normal ventilation (control) and after 1, 2, 3, 4 min of voluntary hyperventilation, after 6 min of hypoxic-hypercapnic ventilation (through an enlarged dead space) and during the Valsalva manoeuvre. The absolute coefficients (a) of the regression lines QT = a + b . HR were significantly different in all groups. The slopes of regression lines (b) were significantly different in all groups with the exception of 4 min hyperventilation. Our results indicate that short-term alterations of pulmonary ventilation may change not only the duration of the QT interval but also its dependence on the heart rate. Voluntary hyperventilation lasting 1-2 min and the Valsalva manoeuvre decrease the rate dependence of the QT interval and this change may cause its prolongation at higher heart rates.