“…Serotonin has been reported in the rat heat (Snyder, Axelrod & Zweig, 1965) bird heart (Sturkie, Woods & Meyer, 1972), and in the heart and blood vessels of sheep (Dyer & Weber,197 1). The major metabolite of serotonin, 5-hydroxyindoleacetic acid has also been reported to be present in the rat heart (Anton & Sayre, 1962).…”