Cardiac macrophages, specialized cells that live in heart tissue, could hold the key to effective new treatments to repair heart damage and remedy erratic heartbeats in patients with arrhythmia, notes Jackson Laboratory Scientific Director and Professor Nadia Rosenthal in a commentary in the July 6 New England Journal of Medicine. Rosenthal points to recent studies establishing cardiac macrophages’ role in maintaining a steady heartbeat, and suggests the possibility of correcting defects in macrophage function leading to arrhythmia (for example, due to infectious disease or diabetes) by immunotherapy that reprograms the macrophages.