Exercise stress tests of the pulmonary circulation show promise for the detection of early or latent pulmonary vascular disease and may help us understand the clinical evolution and effects of treatments in patients with established disease. Exercise stresses the pulmonary circulation through increases in cardiac output and left atrial pressure. Recent studies have shown that exercise-induced increase in pulmonary artery pressure is associated with dyspnea-fatigue symptomatology, validating the notion of exercise-induced pulmonary hypertension. Exercise in established pulmonary hypertension has no diagnostic relevance, but may help in the understanding of changes in functional state and the effects of therapies.