Pulmonary Hypertension (PH) is a condition characterised by increased pulmonary vascular resistance due to pulmonary vasoconstriction and remodelling leading to an increase in afterload on the right ventricle. This manifests as impairment of cardiac output on exercise and as the disease progresses this results in right heart failure and death. As such a cardinal feature of PH is exercise intolerance, usually reported as breathlessness, but presentation is usually relatively late in the overall disease process, by the time pulmonary vascular resistance has increased several fold above normal values. The standard investigations such as lung function and six-minute walk testing may be normal, and exercise testing can be used in breathless patients to point towards a diagnosis of PH which is confirmed by right heart catheterisation. In some cases, resting catheterisation may be relatively normal and stressing the circulation with fluid challenge or exercise may be required to unmask more subtle changes in pulmonary vascular resistance or left ventricular compliance. Once diagnosed, exercise physiology is invaluable in assessing response to therapy and determining therapeutic strategies.