Stem cells in the heart: What's the buzz all about? Part 2: Arrhythmic risks and clinical studies

New approaches for cardiac repair have been enabled by the discovery that the heart contains its own reservoir of stem cells. In Part 1 of this review, we discussed various cardiac stem cell populations, reviewed our own work on cardiosphere-derived cells from human hearts, and outlined large animal preclinical models testing the regenerative potential of cardiac stem cells. Here we continue with a discussion on other adult stem cell sources with clinical potential. We summarize the critical safety issues associated with stem cell therapy and present the possible proarrhythmic and antiarrhythmic effects of stem cell transplantation. We discuss the outcomes of clinical stem cell trials and identify the technical, ethical, and practical issues facing the clinical application of cardiac stem cells.