Primary pulmonary hypertension (PPH) is a rare disease that is characterised by increased pulmonary vascular resistance and arterial pressure, which lead to right heart failure and death. The earliest pathological features of PPH are vasoconstriction and smooth-muscle proliferation. 1, 2 Intracellular Ca2+ is the most important regulator of muscle contraction and cell proliferation. By governing membrane potential, activity of voltage-gated K+ channels (Kv) in pulmonary artery smooth muscle cells (PASMC) is a critical determinant of cytoplasmic free Ca2+ concentration [(Ca2+] cyt), and thus pulmonary vascular tone. 3 Kv channels are composed of pore-forming α subunits (eg, Kv 1· 5) and cytoplasmic regulatory β subunits (eg, Kv β1· 1). 4 Association of regulatory Kv β1· 1 with pore-forming Kv 1· 5 accelerates inactivation of Kv 1· 5 channels and significantly attenuates the amplitude of steady-state Kv 1· 5 channel currents. 4