<qa>  How many subjects were enrolled in the third trial?Clinical trials of pulmonary vasodilator medications in PH of SCD have been problematic. There have been no randomized placebo controlled trials of any traditional pulmonary arterial hypertension PAH medication completed in this population to date 5, 6. Three randomized placebo-controlled trials have been undertaken previously. Two compared treatment with bosentan to placebo in SCD patients with right heart catheterization RHC-defined elevated pulmonary vascular resistance PVR with a normal pulmonary capillary wedge pressure PCWP the ASSET-1 trial or pulmonary venous hypertension PVH with a PVR 100 dynes.seccm5 the ASSET-2 trial 5. After the randomization of only 14 subjects in ASSET-1 and 12 patients in ASSET-2, the trials were prematurely terminated due to slow patient enrollment. Although very few patients were enrolled, there were no apparent toxicity issues. The third trial, Walk-PHaSST Pulmonary Hypertension and Sickle Cell Disease with Sildenafil Therapy 6, compared the safety and efficacy of sildenafil to placebo in SCD patients with a TRV 2.7ms. After 74 of a targeted 132 subjects were enrolled, the study was prematurely discontinued due to an increase in serious adverse events in the sildenafil group, primarily hospitalization for pain. 