They beat like real heart cells, but the rat cardiomyocytes in a dish at Harvard University are different in one crucial way. Snaking through them are wires and transistors that spy on each cell's electrical impulses. In future, the wires might control their behaviour too.
Versions of this souped-up, "cyborg" tissue have been created for neurons, muscle and blood vessels. They could be used to test drugs or as the basis for more biological versions of existing implants such as pacemakers. If signals can also be sent to the cells, cyborg tissue could be used in prosthetics or to create tiny robots.