See Update Below: the larger RELAX trial (enrolling patients with less severe pulmonary hypertension) did not show a benefit of sildenafil. Guazzi et al randomized 44 people with heart failure with preserved ejection fraction and associated pulmonary hypertension (confirmed by right heart catheterization) to receive the phosphodiesterase-5 inhibitor sildenafil or placebo for one year, along with standard therapy. Those in the sildenafil group experienced improvement in cardiac output and reduction in pressures on both the left and right sides of the heart (right atrial pressure, pulmonary artery, pulmonary vascular resistance, and wedge pressures). DLCO also improved. Improved diuresis in the treatment group did not appear to be responsible.