During a routine coronary revascularization procedure in a 51-year-old man, venous return was suddenly interrupted. The venous cannula was rapidly removed, revealing the pulmonary artery catheter wrapped around it. The catheter also had entered the lumen of the cannula, and the inflated balloon completely obstructed the venous return. The prompt removal and reinsertion of the venous cannula resulted in uneventful recovery of the patient.