Summary A 29 year old man with a significant paracetamol overdose was found to have an abnormal electrocardiograph which, in the absence of hepatic encephalopathy, was considered due to a direct cardiotoxic effect of the drug. A functional coronary insufficiency resulting from inhibition of endothelium-derived relaxing factor secondary to depletion of sulphydryl groups is postulated, and it is suggested that in paracetamol poisoning evidence of cardiotoxicity alone may be sufficient justification for treatment with acetylcysteine.