We report a 29 years old female admitted due to a congestive cardiac failure that failed to respond to therapy with furosemide and enalapril. Serum thyroid hormone profile showed a TSH over 40 microIU/ml, a thyroxine of 0.8 microgram/dl and a triiodothyronine below 20 ng/dl. Levothyroxine therapy was started with remission of cardiac failure. The study of thyroid function in patients with cardiac failure of unknown origin and resistant to therapy, should be bone in mind.