The physiological roles of ANG-(3-4) (Val-Tyr), a potent ANG II-derived peptide, remain largely unknown. The present study: (i) investigates whether ANG-(3-4) modulates ouabain-resistant Na⁺-ATPase resident in proximal tubule cells, and (ii) verifies whether its possible action on pumping activity -considered the fine tuner of Na⁺ reabsorption in this nephron segment- depends on blood pressure. ANG-(3-4) inhibited Na⁺-ATPase activity in membranes of spontaneously hypertensive rats (SHR) at nanomolar concentrations, with no effect in Wistar-Kyoto rats (WKY) or on (Na⁺+K⁺)-ATPase. PD123319 (10^-7 M) and PKA_(5-24) (10^-6 M), an AT₂R antagonist and a specific PKA inhibitor respectively, abrogated this inhibition, indicating that AT₂R and PKA are central in this pathway. Despite the lack of effect of ANG-(3-4) when assayed alone in WKY rats, the peptide (10^-8 M) completely blocked stimulation of Na⁺-ATPase induced by 10^-10 M ANG II in normotensive rats through a mechanism that also involves AT₂R and PKA. Tubular membranes from WKY rats had higher levels of AT₂R/AT₁R heterodimers, which remain associated in 10^-10 M ANG II and dissociate to a very low dimerization state upon addition of 10^-8 M ANG-(3-4). This lower level of heterodimers was that found in SHR, and heterodimers did not dissociate when the same concentration of ANG-(3-4) was present. Oral administration of ANG-(3-4) (50 mg/kg body mass) increased [Na⁺]_ur and U_NaV with a simultaneous decrease in systolic arterial pressure in SHR, but not in WKY rats. Thus, the influence of ANG-(3-4) on Na⁺ transport and its hypotensive action depend on receptor association and on blood pressure.