We attempted to use the diving reflex to treat PSVT in five patients, in whom carotid-sinus massage had failed to terminate, PSVT. In three cases PSVT converted to normal sinus rhythm. The patient was seated comfortably, and a pan of ice and water (4 degrees C) was placed on the table in front of the patient. He then took a deep breath and, without expiration, submerged his face in the cold ice and water for about 30 seconds. In case 1, a 68-year-old male, PSVT stopped after facial immersion of 11 seconds. Subsequently, sinus arrest with junctional or ventricular contractions continued for 7 seconds followed by conversion to the sinus rhythm. The duration of facial immersion was 18 seconds. In case 2, a 51-year-old male, PSVT converted to the sinus rhythm in the same way. The duration of facial immersion was 23 seconds. Case 3 was a 27-year-old female with WPW syndrome. PSVT converted to the sinus rhythm after a 6.6 seconds facial immersion. Case 4 and 5 were respectively 72 and 73-year-old males, whose attacks did not respond to the diving reflex for the reason that they could not maintain breath-holding for a sufficient time to activate the reflex adequately. We postulated that apnea might effect the termination of PSVT in case 1 and 2 because relatively long duration of about 20 seconds was necessary to convert PSVT to the sinus rhythm. On the other hand, in case 3, cold water stimulation on the face might play an important role because PSVT converted to the sinus rhythm immediately.(ABSTRACT TRUNCATED AT 250 WORDS)