We Injecte(?) 12-16 ?l 20—40% HRP in normal sanne into the myocardium orthe anterior wall of the left ventricle in six rats and 10 ?l choleragenoid-horsera-dish peroxidase conjugate(CB-HRP)in three rats.The Th1-3 DRG and the nodoseganglia of both side were removed.The sections of these ganglia were proceeded bythe TMB chromogentic reaction for HRP and immunohistochemical reaction(the firstantibody is the substance P antiserum).There are three types of labeled cells——theHRP labeled cells.Sp-IR cells,and HRP-Sp-IR double labeled cells were observedin the Th1-3 DRG and nodose ganglia of both side.The parts of Sp-IR nerve fib-ers in the heart wall originate from the DRG and nodose ganglia and these neuronsprojecting the HRP-Sp-IR nerve fiber contained substanse P.Their functions may berelated to the pain(nociceptive)sensation of the heart.This study may also be aevidence of the main function of the cardiac sympathetic afferent fiber is the con-duction of the pain sensation.A few of HRP-Sp-IR double labeled cells in thenodose ganglion observed suggest that the cardiac parasympathetic afferent fibermay participate in conduction of the pain sensation.This question requires furtherstudy.