After a heart attack, the body’s immune defenses can turn against it: a protein from white blood cells damages heart cells and sparks deadly rhythms. Blocking this molecule could be key to preventing sudden cardiac death. Credit: Shutterstock Nina Kumowski, MD, of the Department of Radiology and Center for Systems Biology at Massachusetts General Hospital, is the lead author and Matthias Nahrendorf, MD, PhD of the Department of Radiology and Center for Systems Biology at MGH, is the senior