Lots of drugmakers know how grueling it can be to wait for FDA decisions on their compounds. But at least CV Therapeutics (Nasdaq: CVTX) can move ahead, now that it has won marketing approval for its cardiac stress agent regadenoson.

The drug, to be marketed under the brand name Lexiscan, helps patients in poor health produce clinically usable heart images for coronary heart disease checkups. Almost a month ago, CVT and North American marketing partner Astellas were set to hear back from the FDA on their scheduled March 14 PDUFA date for regadenoson, but the FDA instead told CVT that its decision on the drug would be delayed.

When the delay was announced, however, CVT also revealed that it was in "final labeling discussions" with the FDA over regadenoson. That's pharma code for "drug approval is on its way."

Astellas says it plans to launch regadenoson soon. The company is an ideal marketing partner for regadenoson, because it also markets King Pharmaceuticals' (NYSE: KG) Adenoscan, which regadenoson was tested against in its phase 3 testing. CVT will gain royalties on the sales, and the numbers could be impressive, considering that King's worldwide Adenoscan royalties were around $82 million last year.

The drug will, however, contend with numerous other long-genericized cardiac stress agents, and it may face an increasingly competitive environment in the coming years, as new generic entries reach the market. King's own second-generation stress agent may gain approval as soon as 2009.

Regadenoson isn't CVT's most important drug, though. That award goes to its angina treatment Ranexa, which is faces several important FDA regulatory decisions in late July. Nonetheless, every bit of extra revenue helps, and the royalties that regadenoson generates should help CVT get that much closer to joining the rare group of profitable pharmaceutical companies.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an A-plus disclosure policy.