After a spate of clinical-trial failures, Pfizer (NYSE: PFE) finally got a win yesterday, when its heart drug Inspra passed its phase 3 trial. Pfizer even saved some money, because the trial was stopped more than a year early because Inspra was clearly working better than placebo.

That's where the good news ends.

Sure, the trial could help Pfizer expand its label for use in more patients. Inspra is approved to help patients with severe heart problems, but this new trial showed that it also helps patients with less-severe heart issues.

But Inspra's sales are essentially nonexistent -- Pfizer doesn't break them out in its regulatory filing -- and they're likely to stay that way. Pfizer claims to have patent protection in some markets, but Novartis (NYSE: NVS) and privately held Apotex both have Food and Drug Administration approvals to sell generic versions in the United States.

Inspra is also approved to treat high blood pressure -- a very large market -- but Pfizer was never able to make the drug work even before it started to see generic competition. It just wasn't up for the strong opposition from GlaxoSmithKline's (NYSE: GSK) Coreg, Novartis' Diovan, Merck's (NYSE: MRK) Cozaar, and Pfizer's own Norvasc.

So why the heck did Pfizer run a trial that's not likely to help it all that much? It's the heart-drug conundrum: Clinical trials need to be big and long, and that makes them high-risk, high-reward propositions. Planning for the recently completed trial began in 2005, when the Inspra's potential still inspired Pfizer.

Five years later, the results aren't good for more than a few positive headlines. At least it didn't take another year to complete the trial.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Pfizer is a Motley Fool Inside Value recommendation. Novartis is a Global Gains pick. The Fool owns shares of GlaxoSmithKline and has a disclosure policy.