1. Cardiovascular Research Center, Massachusetts General Hospital, Charles River Plaza, CPZN 3200, 185 Cambridge Street, Boston, MA 02114–2790, USA.
2. Harvard Stem Cell Institute, Cambridge, MA 02138, USA.
3. Department of Cardiology, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, Netherlands.
4. Disease Biophysics Group, School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
5. The Wyss Institue for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA.
6. Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA 02138, USA.