How do you make heart tissue out of a single cardiac cell in a Petri dish? The answer, it seems, is geometrical. In biology, form dictates function, says Kevin Kit Parker, a faculty member at the Wyss Institute. By designing minute scaffolds to control their geometry, Parker can prod cardiac cells to join together and create tissues that mimic those in a beating heart. Parker’s approach draws from the natural process of self-assembly, which, in this instance, allows cells to aggregate into functional systems by responding to “architectural” cues from their surroundings. In proof-of-principle findings this past year, Parker and his collaborators created a layer of beating heart tissue that can transmit electrical impulses. “Emergent needs for this technology are to engineer tissues useful for drug discovery and safety screening,” says Parker. In the future, he adds, doctors will likely replace damaged heart valves with engineered tissues and implant tissue-engineered pacemakers that don’t need batteries.