A 69-year-old man was hospitalized with HCV infection. The lab findings showed HCV-RNA 1.88×106copies/ml (normal value<2×102copies/ml),ALT 78U/L.The patient had a history of blood transfusion 400ml due to bronchiectasis with hemoptysis in 1984. Liver function test was abnormal. The man was treated with interferon alfa 3 million units by intramuscular injection daily. He suddenly developed palpitation,dizziness, fever and paleness after taking the medication. Physical examination showed body temperature of 38.8℃, HR 140beats/min and arrhythmia while ECG showed atrial fibrillation. Oxygen and cedilanid 0.4mg were administered. 30 minutes later,the symptoms were lessened and normalized gradually. Arrhythmia did not recur after discontinuing interferon alfa. A 69-year-old man was hospitalized with HCV infection. The lab findings showed HCV-RNA 1.88 × 106copies / ml (normal value <2 × 102copies / ml), ALT 78U / L. The patient had a history of blood transfusion 400ml due to bronchiectasis with hemoptysis in 1984. Liver function test was abnormal. The man was treated with interferon alfa 3 million units by intramuscular injection daily. He suddenly developed palpitation, dizziness, fever and paleness after taking the medication. Physical examination showed body temperature of 38.8 ° C, HR 140 beats / min and arrhythmia while ECG showed atrial fibrillation. Oxygen and cedilanid 0.4 mg were administered. 30 minutes later, the symptoms were lessened and normalized gradually. Arrhythmia did not recur after discontinuing interferon alfa.