Conscious dogs were used to study whether changes in total renal hemodynamics are responsible for diuresis and natriuresis during an experimental increase in left atrial pressure (LAP). To ensure a controlled dietary sodium intake, the dogs (n = 8) were chronically kept on a high or a low sodium intake diet (HSI; LSI). After the dogs had completely recovered from surgery (carotid loop, thoracotomy, flank incision), LAP was increased by about 10 cm H2O for 60 min by tightening a purse string around the mitral annulus (51 expts.). Mean urine volume (V) increased in both groups to a comparable degree. Mean sodium excretion increased somewhat more in HSI dogs, but remained elevated in LSI dogs after the LAP increase. Renal blood flow (electromagnetic flow transducer) and inulin clearance did not change. Renal vascular resistance (RVR) increased by about 20% (HSI) and 15% (LSI). --When the induced LAP INCREASE WAS TERMINATED, V decreased. RVR decreased in HSI dogs by about -11% and in LSI dogs by about -6% below control values. --It is concluded that volume regulatory mechanisms induced by an experimental LAP increase operate independently of changes in total renal blood flow.