Atrial myocardial cells store atrial natriuretic factor and secrete the peptide in response to extracellular stimulation. Ventricular myocardial cells also exhibit stimulated secretion of atrial natriuretic factor but with little or no intracellular storage. The stimulated secretion of other proteins from these cells is poorly characterized. In the present study the secretion of sulfated macromolecules from Na2(35)SO4 labeled atrial and ventricular myocardial cells was quantitated. Both cell types secreted a chondroitin sulfate proteoglycan, as evidenced by glycanase digestion. Endothelin-1, a known stimulator of ANF secretion, stimulated secretion from atrial cells about 70% but had no effect on ventricular cell secretion. The differential stimulation of atrial and ventricular cell secretion was not due to the absence of a regulated secretory pathway in the latter cell type since phorbol ester stimulated secretion from both cell types. This result indicates that differences exist in the early steps of signal transduction between atrial and ventricular cells. Pancreastatin, a regulatory peptide derived from chromogranin A, stimulated atrial cell secretion 90%. This result suggests that chromogranin A, which has been identified in atrial secretory granules, may play an autoregulatory role in atrial secretion.