The long-term results of 68 cases of thyrotoxic heart disease (THD) treated with 131I were analysed. 17 of 68 patients have been followed for 2-4 years, 32 for 5-9 years, 7 for 10-14 years, 8 for 15-19 years and 4 for 20-33 years. The mean period of follow up was 9 years. Of the 68 patients, 47 did not respond to antithyroid drug (ATD) therapy. Before 131I therapy, all the patients suffered from one or more of cardiac abnormalities caused by hyperthyroidism such as paroxysmal or permanent atrial fibrillation, cardiac enlargement, cardiac failure, frequent atrial or ventricular extrasystoles, angina pectoris and so on. All patients were given individualized therapeutic 131I dose of 2.59-4.44 MBq per gram of thyroid weight. The total 131I dose for patients was 85.1 MBq to 462.2 MBq. The long-term results showed that 55 cases were cured and 11 cases achieved complete remission. The total effective rate was 97 percent. There was no relapse of hyperthyroidism. Except that 4 cases of early hypothyroidism and 5 of delayed hypothyroidism were diagnosed, there were no other complications. The incidence of postradioiodine hypothyroidism at 5-9 years was 7.4 percent and at 10-33 years 20 percent. Our results indicate that 131I is a simple, safe, economic and effective treatment for THD. Pre-treatment with ATD for hyperthyroidism with cardiac complications is not necessary. 131I should be considered as the treatment of first choice for hyperthyroidism with cardiac abnormalities.