Twenty four myasthenia gravis patients, 14 females and 10 males, aged between 5 and 65 years (average 29) were studied electrocardiographically. The abnormalities found in the ECG were: prolonged "Q-T" intervals (10 cases, 44.1%), sinus tachycardias (5 cases, 20.8%), sinus arrhythmias (5 cases, 20.8%), right bundle branch block (4 cases, 16.6%), and non-specific "T" wave changes (2 cases, 8.3%). Among our 24 patients with myasthenia gravis, in contrast to previous reports, only two had non-specific "T" wave abnormalities. But prolonged "Q-T" intervals, right bundle branch block, sinus tachycardias and sinus arrhythmias, when compared to normal population incidence, were found to be quite significant. In pathogenesis, primary myocardial histo-pathological abnormalities, and the role of extracardiac factors in producing the changes were discussed.