Shares of drugmaker CV Therapeutics (NASDAQ:CVTX) were down nearly 25% today after it announced results from a pivotal clinical study for its heart treatment drug, Ranexa.

In this large phase 3 study, Ranexa was being tested as a treatment for a group of heart ailments known as acute coronary syndromes (ACS). Details in today's press release from CVT were light, but the drug failed to improve clinical outcomes in patients suffering from ACS. On the bright side, management intimated that the drug's safety was not in question, although we'll have to wait until the study's data set is released at a medical conference in three weeks.

Ranexa is already approved and marketed as a treatment for angina (chest pain due to lack of blood and oxygen to heart). In its first partial year on the market in the U.S., sales of the drug were $18 million in 2006, but have been held back due to a restrictive label indicating its use only for patients who don't respond positively to other angina treatments.

If the data from the phase 3 study does truly show Ranexa to be safe and is supportive enough, it could convince the FDA to expand the Ranexa label to front-line use in patients suffering from angina, since CVT had an agreement in place regarding what was needed to get the improved labeling for the drug. A ruling on the drug's marketability in Europe should also come later this year, and if CVT does the sensible thing and finds a marketing partner in Europe, then a partnership agreement could be in the works as well.

Since it often takes the market a while to sort out all of the details of a study and the ensuing upgrades and downgrades that follow, shares whipsaw up and down and sometimes an overreaction occurs. Whether this latest move in CVT shares presents a buying opportunity or not really depends on what the ultimate market potential of Ranexa is. With over nine million angina sufferers in the U.S. alone, though, sales of Ranexa will skyrocket if it gets approved as a front-line therapy for angina.

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