A study of outcomes among 1,200 people with implanted defibrillators — devices intended to prevent sudden cardiac death from abnormal heart rhythms — shows that within a few years of implantation, one in four experienced improvements in heart function substantial enough to put them over the clinical threshold that qualified them to get a defibrillator in the first place. A report on the study reveals these patients had markedly lower risk of dying and were far less likely to suffer arrhythmia-terminating device shocks, suggesting their hearts had grown less prone to developing lethal rhythms.