The myoendocrine cellis a specialized myocyte localized mainly in the right and left atrial appendages, and also scattered within other areas of the atria and along the conductive system in the ventricular septum. The most conspicuous feature distinguishing myoendocrine cells from other atrial myoctyes is the presence of membane-bounded secretory granules (these granules contain precursor of cardiodilatins or atrial natriuretic polypeptides). [ ]