A commonly used erectile dysfunction drug, sildenafil, doesn't help patients who have heart failure with preserved ejection fraction, a condition in which the heart's lower chambers are stiff and cannot relax and fill fully between beats. That is the finding of the RELAX study, presented at the American College of Cardiology's 62nd Annual Scientific Session and simultaneously published in The Journal of the American Medical Association. Sildenafil, a phosphodiesterase-5 inhibitor, had shown encouraging results in smaller studies and in animal models. In this study, researchers looked at the drug's effect on maximum exercise ability as assessed by peak oxygen consumption and on how far people could walk in six minutes, their clinical status and their heart structure and function. They found no benefit, says lead author Margaret Redfield, M.D., heart failure specialist and researcher at Mayo Clinic in Rochester, Minn. "It was surprising and a disappointment, and it was contradictory to our hypothesis," says Dr. Redfield. "There are few options for help for these patients, and we hoped we would find something." When the heart does not pump blood well, heart failure symptoms such as shortness of breath, fatigue and weakness can result.