The authors suggested that these disappointing results were (partially) attributable to the relatively low right-sided heart pressures in their patient group compared with earlier studies in HF with reduced EF (HFrEF); moreover, PDE5 was undetectable in humans or experimental models of HF lysates, whereas it is present in the murine and bovine lung samples which were used as a positive control (Degen et al., 2015). Here, PDE5A is linked to hydrops fetalis.