To assess the effects of mavacamten on health-related quality-of-life (HRQoL) in symptomatic obstructive hypertrophic cardiomyopathy (HCM) and estimate health utilities by New York Heart Association (NYHA) functional class.Patients with symptomatic obstructive HCM were randomized to 30 weeks of mavacamten or to placebo treatment, with or without beta-blocker or calcium channel blocker monotherapy, in EXPLORER-HCM (ClinicalTrials.gov identifier: NCT03470545). Health utility was measured using the EuroQoL 5-dimension 5-level (EQ-5D-5L) index score with the US value set. The 30-week changes in EQ-5D-5L index score and EuroQoL visual analog scale (EQ-VAS) score were compared between the two arms using linear regression, and the proportions of patients with a meaningful improvement were compared using logistic regression. The meaningful change thresholds were estimated using both distribution- and anchor-based approaches. Mean utilities by NYHA class were estimated for each arm using a generalized estimating equation.Compared with placebo (N = 89), patients receiving mavacamten (N = 96) had significantly greater 30-week improvement in EQ-5D-5L index score (mavacamten = 0.084; placebo = 0.009; adjusted difference = 0.073 [95% confidence interval = 0.027-0.118]) and EQ-VAS score (mavacamten = 8.5; placebo = 0.7; adjusted difference = 7.5 [95% confidence interval = 1.8-13.2]), and a significantly higher proportion of these patients showed meaningful improvement in EQ-5D-5L index score and EQ-VAS score. Both outcomes were correlated with the Kansas City Cardiomyopathy Questionnaire Clinical Summary Score (KCCQ CSS) and HCM Symptom Questionnaire Shortness-of-Breath (HCMSQ SoB) subscore, two patient-reported anchor variables. Additionally, mean utilities significantly decreased with higher NYHA functional class (values for NYHA class I, II, and III/IV - mavacamten = 0.950, 0.866, and 0.708; placebo = 0.952, 0.850, and 0.704).Compared with placebo, mavacamten significantly improved EQ-5D-5L index score and EQ-VAS score - and thus HRQoL - among patients with symptomatic obstructive HCM. Patients with a higher NYHA functional class had a lower health utility value.