The race for a new heart treatment has investors thumping their chests over two small biotechs. Some Wall Streeters believe that Encysive Pharmaceuticals ( ENCY) will secure approval for a new drug by the end of this month. Yet shares in rival Myogen ( MYOG) have left Encysive in the dust. Both companies have spent years developing treatments for pulmonary arterial hypertension, or PAH, a rare but potentially fatal disorder affecting the heart and lungs. Encysive hopes to win approval of its PAH drug, known as Thelin, in less than two weeks. But Myogen has convinced investors that its competing drug, ambrisentan, can overcome Thelin's head start because of its superior clinical results. So while Encysive has lost about 20% of its value over the past year, Myogen has rocketed 370%. Encysive CEO Bruce Given said Tuesday that he is surprised by the cold shoulder the market has given his stock. He says company insiders remain "pretty pumped up" during this "very exciting time." Meanwhile, some outsiders have started to question whether Myogen really deserves the favorable treatment. Encysive's stock fell 11 cents to $8.84 on Tuesday, while Myogen's shares continued their climb, rising 92 cents to $36.66. "At current valuations, we believe the market is pricing a best-case scenario for Myogen and a worst-case scenario for Encysive," Oppenheimer & Co. analyst Cory Kasimov wrote last week. "While it is still too early to crown ambrisentan the king of PAH, we concur with popular opinion that recent data could position ambrisentan as a best-in-class drug. ... But we stress that even if ambrisentan does indeed become best-in-class, that does not spell the end for Thelin -- which, we believe, will still be a worthwhile competitor in this rapidly growing market." Matthew Kaplan, an analyst with Punk, Ziegel & Co., has gone a step further by indicating that ambrisentan may not emerge as the clear market winner at all. Notably, he claims that Myogen used less conservative methods for testing the liver toxicity of its PAH treatment than Encysive and another competitor used for their own drugs. Thus, he suggests, ambrisentan may prove to be less safe than it currently seems. While neither Kasimov nor Kaplan has any formal rating on Myogen's stock, both analysts recommend buying Encysive. Their firms both make a market in Encysive securities.