The assessment of exercise capacity is of critical importance in the evaluation and management of patients with moderate to severe pulmonary arterial hypertension (PAH). The practicing clinician uses various exercise modalities in evaluating and managing patients with PAH. These include the 6-minute walk test (6MW), cardiopulmonary exercise testing, and exercise echocardiography. The change in exercise capacity appears to parallel other clinical indicators of disease severity, such as survival, hemodynamics, and time to clinical worsening. Exercise testing can aid the clinician in outlining the nature of a patient's exercise limitation, noninvasively assessing disease severity, establishing prognosis, and evaluating the response to therapy. Additional work must be done to validate the utility of measuring exercise capacity in patients with less severe PAH.