Electrocardiography was used to examine the acute cardiotoxic effects of moniliformin on 3-week-old broiler chickens. Each of the seven pairs of anesthetized birds (pentobarbital sodium, 40 mg/kg body weight, intramuscular) was injected intravenously with moniliformin (1 mg/kg body weight) or an equal volume of normal saline (1 ml/kg body weight), and changes in electrocardiogram were monitored for 50 minutes. Three of the seven birds injected with moniliformin died within 50 minutes post-injection. Moniliformin caused a bradycardia, which became highly significant (P < 0.05) within 15 minutes post-injection. The P-R, Q-T, and S-T intervals of moniliformin-injected birds were significantly lengthened throughout the 50-minute observation (P < 0.05). The results indicate that the moniliformin-induced mortality is due primarily to cardiac failure.