Cultures of neonatal rat heart myoblasts exposed to constant ethanol concentrations of 26, 64, 160 or 400 mg% for 3 days were more arrhythmle during this time than control cultures. Although cell growth was not measurably affected, the evidence suggested that arrhythmlas may have developed from impaired eell-to-ceU contact. Exposure of these treated cells to an arrhythmogenle procedure involving hypoxia and reoxygenatlon, demonstrated a modest antiarrhythmie action of ethanol.