Patients with severe aortic stenosis referred for a clinically ordered right and left heart catheterization will be eligible. Twenty subjects will be enrolled: 10 patients will receive 40mg and 10 patients will receive 80mg; each dose will be equally distributed among those with preserved (≥50%) and reduced (\<50%) EF. Subjects will get a baseline echo prior to the heart catheterization. Baseline invasive hemodynamic measurements will be performed using a Swan Ganz catheter. A single oral dose of sildenafil will then be administered (40mg or 80mg), followed by invasive hemodynamic measurements at 30 and 60 minutes. Also at 60 minutes, limited echocardiographic images will be obtained.
