The contractile apparatus of muscle is a highly efficient and adaptable mechanism for producing movement and is exploited throughout the animal kingdom. Molecular biology is yielding important insights into the intricate functioning of muscular contraction, especially in the heart, and in explaining the genesis of inherited myopathies. Mutational analyses of the sarcomeric-protein genes in conjunction with clinical assessment have shown that certain mutations indicate a more serious prognosis in HCM. Detecting these mutations in individuals is important for screening other family members for the disease. Understanding the contractile apparatus at the molecular level could contribute to the design of more effective drugs for treatment of cardiac diseases.