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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.
After past failures to show a benefit from endothelin antagonists or prostacyclin analogues in PAH due to heart failure, this trial may open the door to wider use of sildenafil for heart failure with preserved ejection fraction with associated pulmonary hypertension. However, it's way too small a sample to draw firm conclusions or change clinical practice.
Wait for results from the larger RELAX trial to help better answer the question of the role of vasodilator therapy for WHO group II pulmonary hypertension (i.e., owing to left heart disease). Circulation 2011;124:164-174.
Update: the larger RELAX trial published in JAMA 2013 showed no benefit of sildenafil in patients with CHF with preserved EF. Almost all of the enrollees had pulmonary hypertension (estimated by echocardiography but unconfirmed by right heart catheterization), with less severe PH than the patients in Guazzi et al. RELAX strongly suggests that there is no benefit of sildenafil in most patients with heart failure with preserved ejection fraction who also have pulmonary hypertension on echocardiography.