To understand the relationship between these novel risk markers in HCM and clinical outcome, the investigators propose a natural history study of 2750 patients with clinically diagnosed HCM studied at baseline with collection of demographic data, clinical risk factors, as well as novel markers from CMR, genotyping, and serum biomarkers of collagen turnover and myocardial injury, enrolled over a 2-year period and followed for 3-5 years (mean of 4 years). The study will be powered to identify risk markers in a Cox model (imaging, serum, and genetic beyond standard clinical risk factors) with a hazard ratio of 1.5 or greater for the primary endpoint, which will be cardiac death (including SCD and HF death), aborted SCD (appropriate discharge of an implantable cardioverter-defibrillator), and need for heart transplantation. Secondary endpoints include all-cause mortality, ventricular tachyarrhythmias, hospitalization for heart failure, atrial fibrillation, and stroke. This study will enable establishment of a predictive model that will help to identify patients at risk as well as patients for future clinical trials to prevent SCD and HF. In addition, it will identify surrogate endpoints to monitor treatment response in HCM.