Little attention has been directed toward the action of atrial peptides on integrated cardiovascular function. In conscious dogs intravenous injection of atriopeptin 24 (10 micrograms/kg) reduced mean arterial pressure (11 +/- 3.2%), mean left atrial pressure (32 +/- 8.6%), left ventricular (LV) end-diastolic pressure (24 +/- 4.3%), and increased heart rate (25 +/- 6.2%). LV dP/dt and stroke volume increased 17 +/- 4.0 and 12 +/- 3.3%, respectively. Cardiac output increased 39 +/- 6.3%. These effects were only acute, lasting less than 10 min. The tachycardia and increase in LV dP/dt were abolished by combined beta-adrenergic and muscarinic cholinergic blocking agents. During an infusion of atriopeptin 24 (10 micrograms X kg-1 X min-1) blood flow, as measured with radioactive microspheres, increased to both the left (101 +/- 35%) and right kidney (122 +/- 37%) and to the spleen (140 +/- 50%). However, blood flow to the stomach, large and small intestine, pancreas, liver, and skeletal muscle did not change, indicating the selectivity of the atriopeptin. Blood flow in the right ventricle, septum, and in all layers of the left ventricle increased slightly, resulting in no change in the endocardial-to-epicardial blood flow ratio most likely due to the changes in myocardial function, i.e., heart rate and stroke volume. Thus, in conscious dogs, atriopeptins increase myocardial performance most likely indirectly secondary to baroreflex unloading after the direct hypotensive effects of atriopeptin 24. This serves to increase cardiac output at a time when renal and splenic blood flows are increased.