A randomized crossover study was done to compare the hemodynamic effects of conventional mechanical ventilation (CMV) and high frequency jet ventilation (HFJV) at comparable levels of alveolar ventilation, Airway pressure, esophageal pressure, and hemodynamic variables using femoral artery and Swan-Ganz catheter were measured during spontaneous ventilation and artificial ventilation with CMV and HFJV, Mean airway pressure and esophageal pressure were significantly lower during HF~JV than during CMV (Paw; 2.22±0.44 vs. 4.12±0.62, Peso; 1.8±0.3 vs. 3.2±0.6). Heart rate, systemic arterial pressure, pulmonary arterial pr re, and pulmonary vascular resistance were not different during both modes of ventilation. Cardiac index, stroke index, and pulmonary artery wedge pressure were significantly higher during HFJV than during CMV (cardiac index; 4.1±0.8 vs. 3.8±0.7, stroke index; 25.0±5.2 vs. 22.8±5.2, PAWP; 3.3±1.4 vs. 2.2±1.3). In conclusion, HFJV produces less hemodynamic impairements and maintains adequate ventilation at lower mean airway pressure and esophageal pressure in normal dogs. This hemodynamic advantage of HFJV is provably related to the lower mean airway pressure produced by HFJV than by CMV.