Na+/H+ exchanger regulation of intracellular pH (pHi) may play a key permissive role in the mitogen-induced vascular smooth muscle cell growth that occurs in systemic and pulmonary vascular remodeling. Spontaneously hypertensive rats (SHR) have increased Na+/H+ exchange in systemic vessels as well as greater systemic vascular remodeling compared with normotensive Wistar-Kyoto rats (WKY). In contrast to WKY, SHR demonstrate only mild pulmonary hypertension and no increased remodeling to hypoxia compared with WKY. We therefore wondered whether Na+/H+ exchange in pulmonary artery smooth muscle (PASM) of SHR might not be elevated compared with WKY. Baseline pHi, Vmax, pK0.5, and Hill coefficient were compared in 12- to 14-wk-old SHR and WKY PASM and aortic smooth muscle (AoSM) segments by ratio fluorescence spectroscopy. The Vmax, pK0.5, and Hill coefficient were significantly increased in SHR AoSM segments compared with WKY AoSM segments (53, 0.55, and 53%, respectively; P < 0.05). There were no differences in these values between SHR and WKY PASM segments, unlike the AoSM segments. We conclude that the Na+/H+ exchanger activity in PASM in the SHR is the same as in the WKY, which is in contrast to systemic arteries where Na+/H+ exchange is greater in the SHR.