Recruitment The investigators will recruit patients with pulmonary hypertension from the National Pulmonary Hypertension Service who are awaiting right and left heart catheterisation studies as part of their routine diagnostic work up. Patients with normal pulmonary pressures will be recruited from patients who are on the waiting list awaiting routine cardiac catheterisation for the investigation of shortness of breath and chest pain. Recruitment will involve a discussion with the patient and printed material that the patient can refer to. They will be fully aware of the additional measurements being made, and no therapeutic promises will be made.