Vitamin D deficiency may play a role in the pathogenesis of chronic heart failure (HF), but whether giving patients supplements to raise vitamin D into the normal range improves their survival is not clear. It has been demonstrated that vitamin D deficiency is common in patients with HF, especially the elderly, in obese and in dark skinned people, and that low vitamin D levels are associated with adverse outcome. The epidemiological data have been confirmed by experimental data, which show that knockout mice for the vitamin D receptor developed myocardial hypertrophy and dysfunction. Data from interventional studies are scarce and discordant, and more research is urgently needed to confirm whether add-on supplementation therapy with vitamin D has a role in the management of patients with chronic HF.