Inclusion Criteria:

• Has completed Study MYK-461-004. Prior participation in a noninterventional observational study is allowed.
• Able to understand and comply with the study procedures, understand the risks involved in the study, and provide written informed consent according to federal, local, and institutional guidelines before the first study-specific procedure.
• Body weight > 45 kg at Screening.
• Has safety laboratory parameters (chemistry and hematology) within normal limits (according to the central laboratory reference range) at Screening; however, a participant with safety laboratory parameters outside normal limits may be included if he or she meets all of the following criteria:
  • The safety laboratory parameter outside normal limits is considered by the Investigator to be clinically unimportant;
  • If there is an alanine aminotransferase (ALT) or aspartate aminotransferase (AST) result, the value must be <3× the upper limit of the laboratory reference range;
  • The body size–adjusted estimated glomerular filtration rate is ≥30 mL/min/1.73 m2.
• Female participants must not be pregnant or lactating and, if sexually active, must use one of the following highly effective birth control methods from the Screening visit through 3 months after the last dose of investigational medicinal product (IMP).
  • Combined (estrogen- and progestogen-containing) hormonal contraception associated with inhibition of ovulation or progestogen-only hormonal contraception associated with inhibition of ovulation by oral, implantable, or injectable route of administration;
  • Intrauterine device (IUD);
  • Intrauterine hormone-releasing system (IUS);
  • Bilateral tubal occlusion;
  • Female is surgically sterile for 6 months or postmenopausal for 1 year. Permanent sterilization includes hysterectomy, bilateral oophorectomy, bilateral salpingectomy, and/or documented bilateral tubal occlusion at least 6 months prior to Screening. Females are considered postmenopausal if they have had amenorrhea for at least 1 year or more following cessation of all exogenous hormonal treatments and follicle-stimulating hormone (FSH) levels are in the postmenopausal range.
• Male partners must also use a contraceptive (e.g., barrier, condom, or vasectomy).

Exclusion Criteria:

• Has QTcF >500 ms or any other ECG abnormality considered by the Investigator to pose a risk to participant safety (eg, second-degree atrioventricular block type II).
• Since enrollment into Study MYK-461-004, has developed obstructive coronary artery disease (>70% stenosis in one or more arteries) or known moderate or severe aortic valve stenosis.
• Since enrollment into Study MYK-461-004, has developed any acute or serious comorbid condition (eg, major infection or hematologic, renal, metabolic, gastrointestinal, or endocrine dysfunction) that, in the opinion of the Investigator or Medical Monitor, would pose a risk to participant safety or interfere with the study evaluation, procedures, or completion.
• Has a positive serologic test at Screening for infection with human immunodeficiency virus, hepatitis C virus, or hepatitis B virus.
• Since enrollment into Study MYK-461-004 has developed clinically significant malignant disease.
• Is taking prohibited concomitant medications; background therapy on beta blockers or calcium channel blockers is allowed as long as the participant has been on a stable dose for at least 14 days prior to Screening.
• Has evidence of current abuse of drugs or alcohol or a history of abuse that, in the Investigator's opinion, would cause the participant to be noncompliant or would otherwise increase the risk to the participant.
• Is unable to comply with the study requirements, including the number of required visits to the clinical site.

Eligibility last updated 0/17/21. Questions regarding updates should be directed to the study team contact.