The clinical features of hyperthyroidism are varied, but bradyarrhythmia and atrioventricular (AV) block are typically not reported in hyperthyroid patients. We present here a case of primary hyperthyroidism with symptomatic high-grade AV block as the sole presenting feature of hyperthyroidism without any obvious precipitating factors for thyroid disease or AV block. This case highlights a rare presentation of high-grade AV block with the risk of progression to complete AV block as a complication of an untreated overactive thyroid.