Mishaps related to valve malfunction in a self-inflating bag-valve unit can lead to fatal complications. We report a case of severe hypotension that resulted from the locking of the Laerdal valve in the inspiratory position during transport in the operating room. A 36 year old man had undergone an off-pump coronary artery bypass graft. Immediately before leaving the operating room, severe hypotension developed abruptly. But an EKG showed only a reduction of heart rate. We started closed cardiac massage with an intravenous bolus injection of epinephrine 0.5 microgram and reconnected the anesthesia breathing circuit. The patient was manually ventilated using the anesthesia reservoir bag. Vital signs immediately recovered. At that time, the patient's abdomen was distended and we suspected an expiratory abnormality. The self-inflating bag-valve unit was tested with an anesthesia reservoir bag as a test lung. Expiration did not occur. Another self-inflating bag-valve unit was substituted and normal ventilation was restored. It is essential that before use, a self-inflating bag-valve unit should be tested for proper function during both expiration and inspiration using a test lung such as, an anesthesia reservoir bag.