Shares of Denver-based Myogen surged in early trading after the biotech announced that its therapy for high blood pressure hit its primary endpoint in improving patients' ability to exercise. Encysive Pharmaceuticals, which is developing a competing product, saw its shares slip on the news. Ambrisentan is being developed to treat pulmonary arterial hypertension which forces the heart to work harder and can lead to a heart attack. Patients involved in a 12-week trial were able to walk significantly farther than patients taking a placebo.

"We believe the robustness of these results is unprecedented for oral therapies for patients with pulmonary arterial hypertension and represents a significant achievement for ambrisentan and Myogen," said J. William Freytag, president and CEO of Myogen.

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