Researchers at Johns Hopkins University have developed virtual replicas of patients' diseased hearts that could guide doctors to better treat them. The custom models were used to block a dangerous irregular heartbeat, a major cause of sudden cardiac arrest, causing about 300,000 U.S. deaths a year. The Food and Drug Administration allowed the technology to guide treatment for just 10 patients. The results suggest that this could improve care for ventricular tachycardia, a difficult-to-treat arrhythmia. The study was published in the New England Journal of Medicine. Researchers are also studying digital twins for cancer care.