PDE5A and heart failure: Sildenafil treatment failed to produce a significant benefit on exercisecapacity among patients with heart failure with preserved ejection fraction after24 weeks of treatment, as demonstrated in the RELAX trial published in 2013 [88].On the other hand, PDE-5 inhibitors have been shown to improve exercise capacityin patients with heart failure with reduced ejection fraction, as documented byrelevant RCTs [89, 90].