The health-related quality of life (HRQOL) and cardiopulmonary exercise testing (CPET) performance of individuals with subclinical and early stage hypertrophic cardiomyopathy (HCM) have not been systematically studied. Improved understanding will inform the natural history of HCM and factors influencing well-being. VANISH trial (Valsartan for Attenuating Disease Evolution in Early Sarcomeric HCM) participants with early stage sarcomeric HCM (primary analysis cohort) and subclinical HCM (sarcomere variant without left ventricular hypertrophy comprising the exploratory cohort) who completed baseline and year 2 HRQOL assessment via the pediatric quality of life inventory and CPET were studied. Metrics correlating with baseline HRQOL and CPET performance were identified. The impact of valsartan treatment on these measures was analyzed in the early stage cohort. Two hundred participants were included: 166 with early stage HCM (mean age, 23±10 years; 40% female; 97% White; and 92% New York Heart Association class I) and 34 subclinical sarcomere variant carriers (mean age, 16±5 years; 50% female; and 100% White). Baseline HRQOL was good in both cohorts, although slightly better in subclinical HCM (composite pediatric quality of life score 84.6±10.6 versus 90.2±9.8; P=0.005). Both cohorts demonstrated mildly reduced functional status (mean percent predicted peak oxygen uptake 73±16 versus 78±12 mL/kg per minute; P=0.18). Percent predicted peak oxygen uptake and peak oxygen pulse correlated with HRQOL. Valsartan improved physical HRQOL in early stage HCM (adjusted mean change in pediatric quality of life score +4.1 versus placebo; P=0.01) but did not significantly impact CPET performance. Functional capacity can be impaired in young, healthy people with early stage HCM, despite New York Heart Association class I status and good HRQOL. Peak oxygen uptake was similarly decreased in subclinical HCM despite normal left ventricular wall thickness and excellent HRQOL. Valsartan improved physical pediatric quality of life scores but did not significantly impact CPET performance. Further studies are needed for validation and to understand how to improve patient experience. URL: https://www.clinicaltrials.gov; Unique identifier: NCT01912534.