Fig. 2 Improvement in exercise tolerance, as measured by 6-minute walk distance. After treatment with endothelin-1 antagonists, distance improved from a mean of 226 ± 159 meters to 351 ± 113 meters (n = 14; P < 0.004). When the 3 patients who had been assigned a walk distance of 0 feet before therapy were omitted from the analysis, the improvement in distance was significant (n = 11; P < 0.019).