MYH6 encodes the myosin heavy chain 6, the major sarcomeric protein responsible for atrial and ventricular muscle contraction through its microfilament motor activity 1. The protein functions as part of the myosin II complex within the myofibril, utilizing ATP hydrolysis to generate the sliding force between thick and thin filaments essential for cardiac muscle contraction 1. Gene expression of MYH6 is developmentally regulated, with a key enhancer controlling the developmental switch from fetal MYH6 expression to adult MYH7 expression; genetic variation disrupting this enhancer-mediated regulation can alter MYH6 expression levels and contractile properties of engineered heart tissues 2. MYH6 mutations contribute significantly to congenital and acquired cardiac disease. Recessive MYH6 genotypes account for approximately 11% of Shone complex cases 3, while MYH6 variants are among the most common incidentally identified DCM-associated genes with substantial pathogenic potential 4. Dominant MYH6 mutations cause familial hypertrophic cardiomyopathy 1, atrial septal defect 3, dilated cardiomyopathy 1EE, and sick sinus syndrome 3. The clinical significance of MYH6 variants lies in their capacity to disrupt fundamental contractile mechanics, with pathogenic variants exhibiting variable penetrance and phenotypic expression depending on genetic background and enhancer function 2.