Using human heart models and experiments with mice, scientists at Johns Hopkins University and Germany’s University of Bonn have shown that beams of light could replace electric shocks in patients suffering from a deadly heart rhythm disorder. Their findings could pave the way for a new type of implantable, optical defibrillators. Current devices deliver pulses of electricity that are extremely painful and can damage heart tissue. The researchers say light-based treatment could provide a safer and gentler remedy for patients at high risk of arrhythmia, an irregular heartbeat that can cause sudden cardiac death within minutes. This idea springs from advances in the field of optogenetics, in which light-sensitive proteins are embedded in living tissue, enabling the use of light sources to modify electrical activity in cells.