Why would the effect of beet root juice on exercise capacity in HFrEF vary with etiology?

We read with interest the work of Coggan et al. published in the Journal of Cardiac Failure (2018; 24:65-73) in February of last year1 with accompanying editorial by Julio Chirinos (2018; 24:74-77)2. Coggan et al. reported that patients with heart failure due to reduced ejection fraction (HFrEF) had an increase in peak oxygen uptake (V ̇O2peak) and peak power output following ingestion of a concentrated beet root juice supplement in a randomized, double-blind, placebo-controlled, cross-over design.
Source: Journal of Cardiac Failure - Category: Cardiology Authors: Source Type: research