In the latest disappointment over cholesterol pill Vytorin, a major European study in patients with heart valve disease found the drug didn't prevent worsening of the disease or lower the need for valve surgery.

Its makers' shares plunged about 15 percent.

Results of a preliminary analysis of the just-completed study showed Vytorin, marketed jointly by Merck & Co. and Schering-Plough Corp., was no better than placebo at lowering the risk of major cardiovascular events - including heart attack, stroke, heart surgery and death - in patients with aortic stenosis.

The sometimes deadly condition, which is becoming increasingly common in elderly people, involves blockage and stiffening of the aortic valve, which sends oxygen-rich blood through the aorta and on throughout the body. More than 5 million Americans have the disease to some extent, and it's the No. 2 cause of heart surgery.

Researchers at 173 sites in Europe were hoping the study, called SEAS, would show Vytorin offers a nonsurgical way to treat aortic stenosis.

That wasn't the case, although Vytorin did cut cholesterol levels about 60 percent.

The findings overshadowed second-quarter results for the two companies, which held up the results from Monday morning until the end of the day.