BACKGROUND: Septal reduction therapy (SRT) provides substantial symptomatic improvement in patients with obstructive hypertrophic cardiomyopathy (HCM). However, long-term disease course after SRT and predictors of adverse outcomes have not been systematically examined. METHODS: Data from 13 high clinical volume HCM centers from the international SHARE (Sarcomeric Human Cardiomyopathy Registry) were analyzed. Patients were followed from the time of SRT until last follow-up or occurrence of heart failure (HF) composite outcome (cardiac transplantation, implantation of a left ventricular assist device, left ventricular ejection fraction <35%, development of New York Heart Association class III or IV symptoms), ventricular arrhythmias composite outcome (sudden cardiac death, resuscitated cardiac arrest, or appropriate implantable cardioverter defibrillator therapy), or HCM-related death. Cox proportional hazards models were used to identify predictors of outcome. RESULTS: Of the 10 225 pat