We describe the case of a 73-year-old woman with liver cirrhosis and hepatocellular carcinoma (HCC) who developed 2 distinct episodes of paroxystic atrial fibrillation (AF) each of which occurred 1 to 4 hours after iodine medium contrast-enhanced computed tomography. Sinus rhythm was restored by amiodarone therapy after the first AF episode and by electrical cardioversion after the second one. A careful clinical, biochemical, and instrumental examination showed that the patient had subclinical hyperthyroidism and moderate mitral insufficiency with mild atrial enlargement.Thus, the coexistence of both subclinical disthyroidism and of cardiac anatomical alterations may have predisposed the patient to AF that in fact occurred when exogenous iodine administration triggered a hyperthyroidism status.