Samples will be collected between 11 am and 1 pm after 30 minutes' supine rest. The samples will be centrifuged and plasma stored at -70°C (peptides) or -20°C (other samples). Plasma [beta]-type natriuretic peptide (BNP) samples will be collected into EDTA and aprotonin and measured by radioimmunoassay 6-minute walk test.