TNNI3K, also known as CARK, is a 936 amino acid serine/threonine-protein kinase that is highly expressed in heart. Overexpression of TNNI3K leads to improved cardiac function by enhancing beating frequency and increasing contractile force and epinephrine response. TNNI3K suppresses phosphorylation of cardiac troponin I and p38/JNK-mediated apoptosis, therefore protecting the myocardium from ischemic injury. Administration of TNNI3K to mice with myocardial infarction improves cardiac performance and attentuates ventricular remodeling, suggesting that TNNI3K could be a promising target in the treatment of cardiac diseases. There are four isoforms of TNNI3K that are produced as a result of alternative splicing events.