Capsaicin is an active component of chili pepper and a pain relief drug. Capsaicin can activate transient receptor potential vanilloid 1 (TRPV1) channels to increase cytosolic Ca2+ concentration ([Ca2+]cyt). A rise in [Ca2+]cyt in pulmonary artery smooth muscle cells (PASMCs) is an important stimulus for pulmonary vasoconstriction and vascular remodeling. In this study, we observed that capsaicin-induced increase in [Ca2+]cyt was significantly enhanced in PASMCs from patients with idiopathic pulmonary arterial hypertension (IPAH) compared with normal PASMCs. In addition, the protein expression level of TRPV1 in IPAH PASMCs was greater than in normal PASMCs. Increasing the temperature from 23ºC to 43ºC, or decreasing extracellular pH value from 7.4 to 5.9, enhanced capsaicin-induced increases in [Ca2+]cyt; the acidity (pH 5.9)- and heat (43ºC)-mediated enhancement of capsaicin-induced [Ca2+]cyt increases were greater in IPAH PASMCs than in normal PASMCs. Decreasing extracellular osmotic pressure from 310 to 200 mOsmol/L also increased [Ca2+]cyt and the hypoosmolarity-induced rise in [Ca2+]cyt was greater in IPAH PASMCs than in normal PASMCs. Inhibition of TRPV1 (with 5'-IRTX or capsazepine) or knockdown of TRPV1 (with shRNA) attenuated capsaicin-, acidity- and osmotic stretch-mediated [Ca2+]cyt increases in IPAH PASMCs. Capsaicin induced phosphorylation of CREB by raising [Ca2+]cyt; the capsaicin-induced CREB phosphorylation was significantly enhanced in IPAH PASMCs compared with normal PASMCs. Pharmacological inhibition and knockdown of TRPV1 attenuated IPAH PASMCs proliferation. Taken together, the capsaicin-mediated [Ca2+]cyt increase due to upregulated TRPV1 may be a critical pathogenic mechanism contributing to the augmented Ca2+ influx and excessive PASMCs proliferation in IPAH patients.