Additional Study Information: The purpose of this study is to compare the effects of Aficamten and placebo on health status and exercise capacity in participants with non-obstructive hypertrophic cardiomyopathy (nHCM). Participation in this research will involve up to 13 visits to the study site. The research study will last between 46 weeks (10.5 months) to at most 82 weeks (19 months). This time estimate includes the screening period(up to 6 weeks) to evaluate if you can participate in the study, the treatment period (36 to 72 weeks), and the follow-up period (of 4 weeks after the last treatment).