The patient was a 55-year-old male with no history of heart diseases. He was administered recombinant IFN α-2b under the diagnosis of chronic hepatitis C. Since sinus Bradycardia (heart rate 40 bpm) appeared in the fourth week of administration (cumulative dose; 240 M.U), IFN was discontinued. Bradycardia was resolved 1 week after discontinuation of IFN and the treatment was resumed with a change of the regimen to IFN-β. Since no bradycardia was noted thereafter, IFN therapy could be completed (total dose; 108 M. U). These observations suggest that the type of IFN or total dose contributed to the appearance of cardiotoxicity.