About half of the cells in an adult heart are cardiac myocytes, or muscle cells, and about half are cardiac fibroblasts or support cells.  Following a heart attack, muscle is lost and fibroblasts form scar tissue.  In his second talk, Srivastava asks whether our understanding of embryonic heart development can be used to reprogram fibroblasts to myocytes to repair damaged adult hearts. His lab showed that introducing the genes for 3 transcription factors important for embryonic cardiac development resulted in an increase in the number of myocytes in a mouse heart after an induced heart attack. Similar results were obtained in vivo in pigs and in vitro in human cells suggesting that in vivo cellular reprogramming by gene therapy has broad implications for organ regeneration.