Results of the multicenter, randomized, controlled trial RELAX were presented at the 2013 ACC Scientific Sessions in San Francisco, USA in early March and simultaneously published online in JAMA. In 216 stable outpatients with heart failure and preserved ejection fraction who were randomly assigned to receive sildenafil or placebo for 24 weeks, the phosphodiesterase-5 inhibitor was not associated with improved peak oxygen consumption (0.20 ml/kg/min reduction for both sildenafil and placebo, P = 0.90), 6-min walk distance (5 m increase for sildenafil vs 15 m increase for placebo, P = 0.92), or clinical status score (94.2 for sildenafil vs 95.8 for placebo, P = 0.85).