We aim to perform a prospective randomised controlled trial to assess the effect of H-ISDN therapy for 6 months on exercise capacity, endothelial function, renal function, clinical outcomes and quality of life (QOL) in Asian patients with CRS. Specifically, we hypothesise that H-ISDN therapy will lead to improvement in exercise capacity (6 minute walk test (6MWT)), endothelial dysfunction (assessed by non-invasive peripheral arterial tonometry(PAT)), renal function, cardiac structure and function, clinical outcomes (all-cause mortality, HF hospitalisations) and QOL in Asian patients with CRS.