INTRODUCTION: One-lung ventilation (OLV), as a model for adult respiratory distress syndrome, was performed in 8 mongrel dogs, which were made a little hypoxemic by adjusting inspired fraction of oxygen (FIO2) in order to know the effect of nitric oxide (NO) on cardiopulmonary hemodynamics and oxygenation during OLV in lateral position. METHODS: Double-lumen endobronchial tube was intubated through tracheostomy. OLV was performed in lateral position by turning to the side where Swan-Ganz catheter tip was located. FIO2 was adjusted to set SpO2 around 85~90%. After stabilization, cardiopulmonary hemodynamic variables and various oxygenation-related parameters were measured respectively at 5 steps: 1) OLV, 2) OLV and 20 PPM of NO inhalation, 3) OLV, 4) OLV and 40 PPM of NO inhalation, 5) OLV. NO (titrated in N2 tank at concentration of 800 PPM) was administered through low-pressure inlet of ventilator and diluted by inspiratory fresh gas. FIO2 setting of ventilator was slightly increased during NO administration to compensate for FIO2 decrease due to NO titration gas (N2) mixing. NO and NO2 concentration was monitored at the inspiratory limb of breathing circuit by a electrochemical analyzer. RESULTS: There were no difference about hemodynamic variables such as blood pressure (BP), pulmonary arterial pressure (PAP), heart rate (HR), central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP). Neither were different calculated hemodynamic variables such as systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), pulmonary perfusion pressure (PPP), cardiac index (CI), and right ventricular stroke work index (RVSWI). PaO2/FIO2, AaDO2, and S/T were significantly different between step 3 and step 4. But other oxygenation-related parameters such as O2, O2 flux, and O2 ER extraction ratio were not different. CONCLUSIONS: NO inhalation may have a potential for relieving hypoxemia during OLV of dogs in lateral position.