Voltage-activated calcium channels are a family of membrane proteins that provide the major influx pathway for calcium in many different types of cells. Calcium-channel blockers inhibit the calcium influx into vascular cells leading to relaxation of smooth muscle cells and vasodilatation. Vasoconstriction of small pulmonary arteries is recognized as a component of the pathogenesis of pulmonary arterial hypertension and treatment with calcium-channel blockers appears to be rational in this setting. No randomized controlled trial has been performed to demonstrate the beneficial effects of calcium-channel blockers in the treatment of patients with pulmonary arterial hypertension. However, uncontrolled studies have suggested that long-term administration of high-dose calcium antagonists dramatically improves survival in a small subset of patients who respond acutely to those drugs, compared with unresponsive patients. The initial response to an acute vasodilator test with inhaled nitric oxide or intravenous prostacyclin or adenosine accurately identifies patients with pulmonary arterial hypertension who are likely to respond to long-term treatment with calcium-channel blockers.