The presence and distribution of the biologically active neuropeptide galanin (GAL), in the rat heart as well as in mouse, guinea pig, rabbit, cat, and dog heart, were analyzed. With some minor variations in the overall distribution, extractable GAL-like immunoreactivity (-LI) was present in all major portions of the heart. In the rat heart, GAL-immunoreactive (GAL-IR) nerve fibers were present in the atria as well as in the ventricles; thin GAL-IR fibers were present in the myocardium as well as around some cardiac blood vessels. A few larger GAL-IR nerve fiber bundles were also present on the surface of the heart. Characterization of extractable GAL-LI in the rat heart, using HPLC, revealed one GAL-IR form, coeluting with synthetic rat GAL. Our findings suggest that galanin is of importance in the control of certain cardiac functions and/or of circulation.