BACKGROUND: High frequency jet ventilation (HFJV) which can be replaced conventional mechanical ventilation (CMV) is another method in respiratory care. But, each one has weakness. This study was designed to determine whether combined HFJV with CMV is more prominent than HFJV on cardiopulmonary system. METHOD: Korean mongrel dogs (n=11) were induced with thiopental sodium 10 mg/Kg, intravenously. Tracheal intubation was performed, and CMV (respiratory rate 30/min, VT 10 ml/Kg, FiO2 1.0) was applied. After placement of monitors, arterial blood pressure (BP), heart rate (HR), central venous pressure (CVP), cardiac output (CO), pulmonary capillary wedge pressure (PCWP) were measured for control values on steady state of vital signs. Thereafter, HFJV was done using respiratory rate 120/min, inspiratory time 30 %, driving pressure 40 psi for 60 min (examed at time of 15, 30, 60 min), and then CMV was supplemented to HFJV using VT 10 ml/Kg, respiratory rate 8, 4, 2, 1, 0.5/min for 150 min (examed at time of 30, 60, 90, 120, 150 min). All values were measured and analyzed on suggested times according to the different ventilatory modes. RESULT: Arterial BP, HR, CO, CVP and PCWP were not changed significantly during the 60 minutes of HFJV. PaCO2 was increased significantly from 33+/-9 mmHg to 45+/-12 mmHg (p<0.05) and arterial pH was decreased significantly from 7.39+/-0.10 to 7.29+/-0.11 (p<0.05) after 60 minutes of HFJV. PaO2 was not changed for HFJV. Variables (BP, HR, CO, CVP and PCWP) were not changed significantly after combined HFJV with CMV at each respiratiry rates. Elevated PaCO2 at the 60 minutes of HFJV was normalized after combined HFJV with CMV at respiratory rate of 8, 4, 2, 1, 0.5/min. (p<0.05) and decreased pHa was also normalized (p<0.05) after combined HFJV with CMV at respiratory rate of 8, 4, 2, 1/min. PaO2 was not changed for the time which we combind HFJV with CMV. CONCLUSION: The combinded HFJV with CMV makes expected arterial oxygenation and prevents accumulation of arterial carbon dioxide without depressive effect on cardiovascular system, when tidal volume of CMV is 10 ml/Kg and the respiratory rate is above 1/minute. So, this study suggests that the combined HFJV with CMV may be applied to respiratory failure effectively.