Of note, Hbmass, rather than Hb concentration, is a crucial determinant of maximal oxygen consumption (VO2max), a hallmark of exercise tolerance routinely used to ascertain cardiac transplant eligibility in patients with advanced HF (Montero et al. 2015; Montero and Flammer 2017; Lundby et al. 2017). The gene discussed is GSTM1; the disease is hydrops fetalis.