Balloon-tipped, flow-directed (Swan-Ganz) catheters are used commonly for monitoring of cardiac function in patients undergoing cardiac surgical procedures. We report a case of pulmonary hypertension with hypoxemia which may be caused by incorrect positioning of pulmonary artery catheter (PAC) during CABG. Pulmonary arterial pressure (PAP) of 70/40 mmHg which was nearly high as systemic pressure was measured when we tried to wean patient from cardiopulmonary bypass. But, TEE (transesophageal echocardiography) showed nonspecific finding. PAP decreased soon and maintained about 33/16 mmHg for a few minutes. But, the PAP elevated high to 70/40 mmHg again and the arteral oxygen tension (PaO2) decreased to 61.2 mmHg. When we withdrew the PAC to the depth of 35 cm, the PAP and systolic pressure returned to normal range and PaO2 elevaed to 320 mmHg. End tidal CO2 was elevated from 30 mmHg to 35 mmHg.