Cell-based therapy is a promising option for treatment of ischemic diseases. Several cell types have experimentally been shown to increase the functional recovery of the heart after ischemia by physically forming new blood vessels, differentiating to cardiac myocytes and--additionally or alternatively--by providing proangiogenic and antiapoptotic factors promoting tissue repair in a paracrine manner. Clinical studies preferentially used adult bone marrow-derived cells for the treatment of patients with acute myocardial infarction. Most of the studies suggested that cell therapy reduced the infarct size and improved cardiac contractile function. However, cell therapy is in its early stages, and various questions remain. For example, the identification of those patients who benefit most from cell therapy, the optimal cell type and number for patient with acute and chronic diseases, the best time and way of cell delivery, and the mechanisms of action by which cells exhibit beneficial effects, need to be further evaluated. Although no major safety concerns were raised during the initial clinical trials, several potential side effects need to be carefully monitored. The present review article summarizes the results of the clinical studies and discusses the open issues.