This case report concerns a hemodialysis patient with arrhythmia. A 71-year-old man had undergone hemodiafiltration (HDF) for 17 years for the treatment of chronic glomerulonephritis. Because of repeated heart failure and chronic atrial fibrillation, he could not continue receiving standard hemodialysis, which is hemodialysis using bicarbonate dialysate including a small amount of acetate. Neither elevating the sodium concentration of the dialysate nor changing the HDF modality was effective. Acetate-free biofiltration (AFB) was initiated and this treatment dramatically ameliorated the patient's intradialytic acute hypotension and arrhythmia. The patient's quality of life subsequently improved and his scores on the Short-form 36 questionnaire (a measure of quality of life) increased. AFB is an HDF technique based on the continuous postdilution infusion of a sterile isotonic bicarbonate solution. Previous studies have reported that acetate induces chemical cytokines and vasodilator substances. AFB may be effective for preventing acute hypotension and arrhythmia during dialysis and may improve quality of life, including mental status.