Within the quiet architecture of the mouse heart lies a small but sovereign nervous system — one that science is only now beginning to read with precision. Researchers have identified two distinct populations of nerve cells that divide the labor of cardiac survival: one governing the steady rhythms of daily life, the other standing guard against electrical catastrophe under duress. Published in Cell, the findings suggest that the heart's inner intelligence is not a single voice but a conversation — and that future medicine may learn to address each speaker separately.