The cardiac response to dietary salt loading was assessed by Doppler echocardiography during various sodium intakes (52-345 mEg per day) in 30 patients with essential hypertension. The Mitral flow velocity integral in the rapid filling phase (IntR) and the atrial contraction phase (IntA) was measured from the transmitral flow pattern, and the sum of IntR and IntA (IntR + IntA), the ratio of IntA to IntR (IntA/IntR), cardiac output (CO) and total peripheral resistance (TPR) were calculated. With salt loading, the mitral flow pattern remained almost unchanged in the nonsalt-sensitive (NSS) patients. Fourteen of the 19 salt-sensitive (SS) patients showed significant increases in IntR + IntA and CO with salt loading (IntR + IntA, from 13.9 +/- 2.8 to 17.9 +/- 3.6 cm, p less than 0.01; CO, from 6021 +/- 2130 to 8305 +/- 1699 ml/min, p less than 0.01), and were termed "salt-sensitive CO-dependent" (SS [COdep]), suggesting that the apparent pressor response to sodium loading was mediated by an increased CO. In the remaining five SS patients termed "salt-sensitive CO-independent" (SS [COindep]), IntA/IntR increased significantly with sodium repletion (from 0.66 +/- 0.23 to 0.90 +/- 0.31, p less than 0.01), without a significant change in IntR + IntA. Increments in IntA/IntR observed in the SS [COindep] patients were considered to be due to an elevation of total peripheral resistance (TPR), since changes in IntA/IntR were significantly correlated with those in TPR in all subjects (r = 0.617, p less than 0.01).