Objectives To determine the incidence of ECG abnormalities in a healthy adults undergoing a surgical extraction of third molar teeth pre- and post-operatively and to study the effect of local anaesthetics, surgical stress and analgesics on cardiac rhythm. Method One hundred and ninety-eight healthy adult patients taking part in a clinical trial of analgesics were randomly selected for this study. All patients required the removal of at least one impacted mandibular wisdom tooth under local anaesthetic. An ECG was taken at a screening visit and repeated post-operatively 30 minutes after analgesia was given. The effects of analgesia were also monitored to ascertain whether any changes were related to pain experience or the analgesic itself. Results ECG abnormalities were detected in 44 patients at the screening visit. Of these patients, 20 showed rsR complex patterns, seven showed non-specific ST elevation, six patients had an abnormal P wave axis, three patients presented with single atrial premature beats and three patients showed a short PR interval. Other minor abnormalities were occasionally seen. The results recorded were of minimal clinical significance and the numbers are in line with previous research. Post-operative abnormalities were seen in 60 patients. Nineteen patients showed rsR complex patterns, sinus arrhythmias were seen in 11 individuals, seven patients showed non-specific ST elevation and six patients had an abnormal P-wave axis. Other minor abnormalities were occasionally seen. Conclusion Although the results were not statistically significant, some of the patients did show clinically relevant abnormalities which necessitated referral to a cardiologist. These included: marked ST elevation; marked ST depression and one case of Right Bundle Branch Block (RBBB).