Cardiomyopathies are diseases of heart muscle that are associated with cardiac dysfunction. Molecular ge- netic studies performed to date have demonstrated that the damage or mutations in several sarcomeric contractile protein genes are associated with the development of the diseases. In this review, cardiac troponin I, one of the sarcomeric thin filament protein, will be discussed regarding its role in cardiac function, its deficiency-related diastolic dysfunction, and the mutation of this protein-mediated restrictive cardiomyopathy. Cardiomyopathies are diseases of heart muscle that are associated with cardiac dysfunction. Molecular ge netic studies performed to date have the same damage the mutations in several sarcomeric contractile protein genes are associated with the development of the diseases. In this review, cardiac troponin I , of one of the sarcomes be discussed regarding its role in cardiac function, its deficiency-related diastolic dysfunction, and the mutation of this protein-mediated restrictive cardiomyopathy.