Troponin Troponin is a muscle protein present in cardiac and skeletal muscle. Troponin is a complex of three proteins, troponin C, troponin T and troponin I. The complex is located on the thin filament of the sarcomere and is involved in the regulation of muscle contraction. Cardiac troponins Cardiac isoforms exist of troponin T and troponin I. Antibodies have been raised against these cardiac isoforms. The presence of a rised cardiac troponin in serum or plasma indicates cardiac cellular damage.