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We report the case of a 59-year-old man with a dilated nonischemiccardiomyopathy who had chronic rapid atrial fibrillation despite severaltherapies. Radiofrequency modification of the atrioventricular (AV) junctionslowed the mean ventricular rate from 120 beats per minute (bpm) to 60 bpm.Five hours after the procedure and during the following 1 week, despiteventricular pacing at 90 bpm, the patient developed nonsustained orsustained polymorphic ventricular tachycardias. Finally, pacing at 90 bpmwas successfully used in this patient. In conclusion, patients who haveundergone modification of AV conduction may be at high risk oflife-threatening ventricular arrhythmias in the first week following theprocedure.