Described as secreting a mouse monoclonal antibody (IgG2b) reacting with fetal, neonatal and adult cardiac fibers in immunofluorescence and with rat cardiac fetal and adult troponin T in Western blotting; in immunofluorescence this antibody stains some rat fetal and neonatal skeletal muscle fibers which express fetal cardiac troponin T as also shown by the Western blotting of rat fetal and neonatal skeletal muscle; this cell line was produced by fusing NSO myeloma cells with spleen cells from a Balb/c mouse that had been immunized with a myofibrillar preparation from hypothyroid rabbit ventricle