Citation1, Citation2 However, there is not yet proof-of-concept that stem cells can regenerate substantially damaged hearts in humans. In some vertebrates such as zebrafish and newts cardiac regeneration was documented after severe injury based on division of cardiomyocytes. In future we need in this important field of regenerative medicine: i) more experimental data in large animals that are closer to the anatomy and physiology of humans, including data on dose effects, comparison of different cell types and different delivery routes ii) a better understanding of the molecular mechanisms involved in the fate of transplanted cells iii) more intensive research on genuine regenerative medicine, applying genetic regulation and cell engineering. Even the effectiveness of cell therapy in these approaches is doubtful. However, there are no solid data showing that any of these approaches can regenerate human myocardium.

Despite these weaknesses results of several clinical trials including several hundreds of patients with ischemic heart disease have been published.

Moreover, the reproducibility of these results in precisely translated large animal models is still less well investigated. However, these experiments revealed controversial results on transdifferentiation vs transfusion of adult stem cells vs paracrine effects of these cells, which is still being debated.

The basic mechanisms have been studied mostly in murine models.

The recent identification of bone marrow-derived adult stem cells and other types of stem cells that could improve heart function after transplantation have raised high expectations.

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