Design This protocol will involve passing catheters as per usual practice into the pulmonary arteries and aorta. A Combiwire (a standard pressure and flow measurement wire which has been available commercially and used worldwide for the past 5 years for making physiological measurements in the coronary arteries) will then be advanced approximately 1cm beyond the end of the catheter. Participants will have the usual clinical protocol of left and right heart catheterisation (and coronary angiography if clinically indicated) and the simultaneous pressure and flow measurements will be made in addition. Participants will also have noninvasive imaging (echocardiography and, if clinically indicated, cardiac MRI) and serum biochemical measures, as per usual clinical practice. They will also undergo cardiopulmonary exercise testing to assess their lung and cardiac capacity.