Conventional wisdom states that the heart cannot regenerate because cardiac myocytes — unlike cells in the bone marrow or intestinal epithelium — cannot divide. But, in 3 January New England Journal of Medicine, Federico Quaini and colleagues from New York Medical College, US investigated heart transplants from eight female donor hearts into male recipients (NEJM 2002, 346:5-15). This type of cross-gender transplant provides a unique opportunity to determine whether host cells have migrated by testing for presence of the Y chromosome.

In post-mortem analysis, the atria of the recipient heart and the atria and ventricles of the graft were examined by immunofluorescence to determine whether Y chromosomes were present in the transplanted hearts. They showed that 7-10% of myocytes, coronary arterioles and capillaries in the donor hearts bore Y chromosomes.

Quaini et al. further investigated if host primitive cells had arisen from host myocardial tissue...