Little is known about mental stress effects on the pulmonary circulation in health and disease. The current study was conducted to investigate whether pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) would further increase during standardized mental stress testing in patients with severe pulmonary hypertension. The study was a prospective analysis of seven patients (average age: 40 years, range from 21 to 56 years) with severe pulmonary hypertension (primary: n = 4, secondary forms: n = 3; resting mean pulmonary artery pressure ranged between 48 and 65 mmHg). Right heart catheterization for the determination of PAP, pulmonary capillary wedge pressure (PCW) and cardiac output (CO) was clinically indicated (diagnostic workup, acute drug testing). Patients accomplished a standardized 10 min mental stress test (computer based, adaptive complex reaction-time task). Pulmonary haemodynamics during stress were compared to resting baseline. During mental stress mean PAP (+/- SEM) increased by 9.4 +/- 2.1 mmHg (P < 0.005). Pulmonary vascular resistance increased by 149 +/- 25 dyne s cm-5 (P < 0.001). Stroke volume decreased by 6.6 +/- 2.2 ml (P < 0.03). The data show that moderate mental stress increases right heart afterload in patients with severe pulmonary hypertension owing to elevation of PVR.