120 cases of class IC antiarrhythmic overdose, including propafenone, flecainide, ajmaline and prajmaline overdose, were evaluated with respect to clinical course, therapy and outcome. Whereas drug overdose in general has an overall mortality of less than 1%, intoxication with antiarrhythmic drugs of class IC was associated with a mean mortality of 22.5%. Nausea, which occurred within the first 30 minutes after ingestion, was the earliest symptom. Spontaneous vomiting probably led to self-detoxication in about half the patients. Cardiac symptoms including bradycardia and, less frequently, tachyrhythmia occurred after about 30 minutes to 2 hours. Therapeutic measures included administration of activated charcoal, gastric lavage and a saline laxative, catecholamines, and in some patients, hypertonic sodium bicarbonate, insertion of a transvenous pacemaker and hemoperfusion. Fatal outcome was mainly due to cardiac conduction disturbances progressing to electromechanical dissociation or asystolia. Resuscitation, which had to be performed in 29 patients, was successful in only two of them. No correlation was found between fatal outcome, the type of antiarrhythmic, and ingested dose. Since a specific treatment is not available and resuscitive procedures including sodium bicarbonate and insertion of a pacemaker are of limited therapeutic value, early diagnosis and primary detoxification are most important for prevention of fatal outcome.