In this first clinical study of a new mode of ventilation, called intermittent high frequency ventilation (IHFV), a comparison was made in ten patients after myocardial revascularization, between normal ventilation, high frequency ventilation (HFV) and IHFV at 15, 60, 100 and 160 breaths per min (b.p.m.). During IHFV the ventilation was interrupted for 3 s 7 times per min. The measured mean trapped gas volumes were 219 ml at 60 b.p.m. and 716 ml at 160 b.p.m. At 160 b.p.m. during IHFV, the mean, mean airway pressures, pulmonary artery (PAP) and capillary wedge pressures and the Paco2 were decreased, while the cardiac output increased. When the Paco2 was maintained constant, IHFV also allowed a reduction in the mean peak and mean airway pressures. This new mode of ventilation can prevent sustained increases in the lung volume and provide a reduction in intrapulmonary pressures. It also permits the measurement of the trapped gas volume and end-tidal CO2 gas concentrations several times a minute for the clinical management of patients during high frequency ventilation.