Thyroid hormones play an important role in regulating different functions regarding metabolism and performance in multiple organs. Any change in the thyroid hormones axis can lead to profound effect on the vital organ stability especially the cardiovascular system. Hypothyroidism is classified according to the clinical presentation as overt and subclinical. Currently, there exists a paucity of evidence on the beneficial effects of thyroxine hormone replacement on cardiovascular mortality outcomes in subclinical hypothyroidism. Also, the clinical relevance of measuring and treating supra-normal thyroid-stimulating hormone levels in newly diagnosed heart failure patients with preserved ejection fraction requires further study. Here we review the current evidence regarding the prognostic significance of sub-clinical hypothyroidism in patients with heart failure with preserved ejection fraction.