The most common electrocardiographic findings inhyperthyroid patients are sinus tachycardia and short-ening of the PR interval. Despite the improvement inatrioventricular conduction, intra-atrial and intraven-tricular conduction disturbances occasionally result.More frequent is the prolongation of intra-atrial con-duction as evidenced by an increase in P-wave dura-tion. Intraventricular conduction delay in the form ofright bundle branch block is seen in around 15% ofpatients, while atrioventricular block may also occur,for reasons unknown. In addition, hyperthyroidismmay lead to early atrial systoles, paroxysmal supra-ventricular tachycardia, atrial fibrillation and atrial22most common cardiac complication of hyperthyroi-dism. It occurs in 5-15% of cases and is usually ac-companied by a rapid ventricular response. It is morecommon in men, and its incidence increases signifi-cantly with age, while it is rarely found in men agedTSH do not develop overt hyperthyroidism.quently, the risk of atrial fibrillation in patients with subclinical hyperthyroidism is the same as in patients with clinical hyperthyroidism.Heart failureflutter.Among these arrhythmias, atrial fibrillation is the