The authors briefly review the biological effects of vitamin D on the heart and discuss the experimental and clinical studies related to the potential protective effect of vitamin D on the cardiovascular system. Experimental and observational studies in man strongly suggest that vitamin D supplementation can benefit heart failure patients and improve cardiovascular health in the population. However, presently there are limited randomized controlled studies. The authors highlight the hypothesis that vitamin D-induced mechanisms activating calcium channels may represent a novel target for therapy in patients with heart failure.