Methods: Patients will undergo an initial CPET and will then be randomized to receive either beetroot juice (BRJ, containing NO3-, 6.2 mmol/day, administered as 500ml Beet it Sport Shots, James White drinks, Ipswich uk) or 'placebo' (PL, NO3-depleted beetroot juice) for 7 days. A second CPET will then be performed.