The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics (the levels of drug in the blood) and pharmacodynamics (the effect of the drug on your body) of the study drug, MYK-491, when administered orally twice a day for about one to two weeks.The study will recruit patients with an enlarged heart and weakened heart muscle not caused by heart damage from a heart attack or heart valve problem. Eligible patients must also have a specific genetic mutation called MHY7. All subjects that qualify will receive MYK-491 (no placebo, or inactive pill will be dispensed during the study). The study medication is designed to improve cardiac contractility or the ability of the heart to squeeze.

This study has two treatment periods during which multiple doses of MYK-491 (the study drug) will be administered. Once Treatment Period 1 is completed, participants will return to the clinical site for study assessments and to obtain a dose for Treatment Period 2. The investigator will review the results of the study assessments and participants will learn if they will receive a lower or higher dose of MYK-491 for Treatment Period 2 than they received in Treatment Period 1. The expected study duration ranges from about 4 weeks to 11 weeks, including about 1-8 weeks for screening, 9 to 15 days for IMP dosing and an approximately 1 week (7±1 days) follow-up visit.

The purpose of this research study is to test if ARRY-371797 (PF-07265803) is safe and effective in treating dilated cardiomyopathy caused by a genetic mutation to the LMNA gene. This will be demonstrated by the functional capacity of patients in their 6-minute walk tests and quality of life questionnaires.

The purpose of this study is to identify gene changes that cause DCM and gene differences that influence the development and severity of DCM. These genetic studies may identify a change in a gene that has already been linked with DCM, a change in a gene not previously associated with DCM, or these studies may identify a gene or genes that affect the development and severity of the DCM. With this knowledge we hope to have a better understanding of how genes and gene changes cause DCM.