Three potential options are cardiopulmonary exercise testing (CPET), which is often considered to be the ‘gold standard’ non-invasive assessment of functional capacity; the Duke Activity Status Index (DASI),13 which is a standardised questionnaire with demonstrated correlation to gold standard measures of functional capacity; and the serum concentration of N-terminal pro-B-type natriuretic peptide (NT pro-BNP), which is biomarker for heart failure or cardiac ischaemia. Here, NPPB is linked to heart failure.