Cardiovascular manifestations in thyroid disorders are frequently encountered in clinical practice. Thyrotoxicosis commonly causes sinus tachycardia. The development of atrioventricular (AV) conduction disorders, particularly heart block, especially in hyperthyroidism is rare. The author reports 2 cases with thyroid function disorders presenting as complete AV block, and how they were managed. There are some proposed mechanisms for AV blocks in hyperthyroidism but the exact mechanisms for AV blocks in hyperthyroidism but the exact mechanism is still unknown.