The promise of embryonic stem cells lies in their ability to develop into any type of cell in the human body, which should allow us to replace tissues lost due to injury or disease. But it's one thing to generate replacement cells; it's another thing to generate entire tissues and integrate them into a functioning organ. A paper released by Nature now reports some success with turning human embryonic stem cells (hESCs) into cardiac cells and getting them to beat in synchrony with a damaged heart.