For more than half a century, lithium has been one of the most reliable treatments for bipolar disorder. It has given countless people the ability to stabilize their moods and reclaim lives otherwise disrupted by cycles of mania and depression. But lithium comes with inherent risk: its therapeutic range is narrow, which means that the difference between a helpful dose and a harmful one is surprisingly small. Too much lithium in the body can lead to a cascade of health problems, including neurological confusion, tremors, kidney dysfunction, and, though much less well known, potentially dangerous effects on the heart. In a recent publication, Dr. Jeffrey Curran Henson of the University of Arkansas for Medical Sciences, and colleagues, shed light on one of lithium’s most alarming but underappreciated risks: its ability to disrupt the heart’s natural pacemaker, the sinus node. Their case study and systematic review tell the story of a patient whose life was threatened not by the mental illness she had long managed, but by the very medication that had allowed her to manage it. And in that story, the researchers also describe a novel way out: a treatment that avoided the need for invasive procedures and could reshape how we think about emergency care for lithium-related heart complications.