We studied the effects of pretreatment with hypertonic solutions on the conduction disturbances and cardiac arrhythmias caused by iv injection of bupivacaine in anesthetized mongrel dogs. Bupivacaine was injected in doses of 3 mg/kg and 6.5 mg/kg. The hypertonic solutions used were: 7.5% NaCl, 5.4% LiCl, 50% Glucose (5 ml/kg) and 20% mannitol (10 ml/kg). Bupivacaine induced severe conduction disturbances, as reflected by significant increases in QRS complex duration, HV interval and IV interval, and severe hypotension. The arrhythmias observed were: sinus node dysfunction, nonsustained ventricular tachycardia, sustained ventricular tachycardia and ventricular fibrillation. These effects were dose dependent, and were more evident with the higher dose of bupivacaine. Among all the hypertonic solutions tested, only 7.5% NaCl effectively protected against conduction disturbances and cardiac arrhythmias. These findings suggest an important role for sodium overload in these situations and provide a potentially harmless tool for the treatment of anesthetic accidents with bupivacaine during regional anesthesia.