IntroductionThyroid hormones plays key role in regulating cardiovascular system. Its imbalance leads to various electrophysiological changes in cardiovascular system. This study was done to determine the frequency of electrocardiographic (ECG) changes in patients with primary hyperthyroidism.MethodsIt was a descriptive cross-sectional study conducted in the Department of Medicine, Medical Unit III, Ward-7, Jinnah Postgraduate Medical Centre, Karachi, from October 2013 to April 2014. A total of 103 patients newly diagnosed with primary hyperthyroidism were included in this study. Venous blood samples were collected for T3, T3, TSH analyzed by radioimmunoassay. ECG was performed. Outcome variables were the ECG changes i.e. sinus tachycardia and atrial fibrillation.ResultsThe average age of the patients was 30.09±5.57 years (95%CI: 29 to 31.18). Out of 103 cases, 19 (18.45%) were male and 84 (81.55%) were female. Sinus tachycardia was observed in 60.19% (62/103) patients whereas atrial fibrillation was found in 11.65 (12/103) of cases.ConclusionIn this study frequency of electrocardiographic changes in term of sinus tachycardia was high. This report has emphasized the importance of thyrotoxicosis as a cause of cardiac morbidity and mortality in patients with thyrotoxicosis. These cardiac complications are readily reversible if timely optimal treatment is offered.