A thyroid storm is a rare manifestation of thyrotoxicosis and usually occurs in females during the third to sixth decades of life. Serious complications such as heart failure and hypotension resulting from cardiac arrest may occur. We describe two cases of young females who suffered from thyroid storms with thyrotoxic cardiac failure. Severe pulmonary edema and respiratory failure presented in the first patient who had previously received a subtotal thyroidectomy. Decompensated diabetic ketoacidosis presented in the second patient. Both of them were complicated by sudden cardiac arrest and the patients were successfully resuscitated with a good outcome after aggressive management.