Background: Abnormalities in thyroid function are frequent in patients with heart failure and are associated with increased mortality. However, the relation between thyroid hormone levels and echocardiographic parameters has not been investigated sufficiently. Aim: The aims of this study were to investigate the correlations of thyroid hormone levels with echocardiographic parameters and to evaluate their associations with subsequent mortality in a group of patients with dilated cardiomyopathy (DCMP). Methods: Serum levels of thyroid hormones were measured in 111 consecutive patients with DCMP (35 female, 76 male, mean age: 62 12 years). All patients underwent echocardiographic examination and were followed-up for a period of 12+/-8 months. Results: Twenty-three patients (21%) had abnormalities in thyroid function tests. Free triiodothyronine (fT3)/free thyroxine (fT4) ratio was significantly correlated with most of echocardiographic parameters, such as chamber diameters and ejection fraction. Sixteen patients (14%) died during the follow-up period; their fT3/fr4 ratio was significantly lower than the patients who survived (1.31 +/- 0.37 vs. 2.01 +/- 0.72, p < 0.001). A fT3/fT4 ratio of less than or equal to 1.7 was associated with an increased risk of mortality (p < 0.001), independent of other prognostic markers. Sensitivity, specificity, positive and negative predictivity of fT3/fT4 ratio less than or equal to 1.7 for cardiac mortality were 100%, 71%, 36% and 100%, respectively. Conclusion: Determination of FT3/FT4 ratio may be a valuable and simple predictor for identification of patients with DCMP who are at high risk of subsequent mortality. (C) 2004 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.