The primary objective is to perform a pilot study in patients with hypertrophic cardiomyopathy (HCM) and mutations in genes encoding sarcomere proteins to assess safety and gather the pre-requisite data for subsequent robust randomized placebo-controlled efficacy studies with N-acetylcysteine (NAC). We will gather data on the recruitment, accrual, retention, and compliance rates of HCM patients randomized to treatment with a placebo or two escalating doses of NAC. Likewise, we will determine any potential side effects and estimate the effect size of NAC on indices of cardiac hypertrophy.