Cardiac-restricted genes play important roles in cardiovascular system. In an effort to identify such novel genes we identified a novel cardiac-specific kinase gene TNNI3K localized on 1p31.1 based on bioinformatics analyses. Sequence analysis suggested that TNNI3K is a distant family member of integrin-linked kinase. Northern blot and 76-tissue array analyses showed that TNNI3K is highly expressed in heart, but is undetectable in other tissues. Immunohistochemical analysis predominantly localized TNNI3K in the nucleus of cardiac myocytes. In vitro kinase assay showed that TNNI3K is a functional kinase. The yeast two-hybrid system showed that TNNI3K could directly interact with cardiac troponin I, results that were further confirmed by coimmunoprecipitation in vivo. Our data suggest that TNNI3K is a cardiac-specific kinase and play important roles in cardiac system.