Merck & Co Inc, in the latest disappointment for its roster of experimental drugs, said on Friday its high-profile drug meant to treat heart failure missed goals of a pivotal late-stage study.

Merck, whose shares fell 1.6 percent, said it will not file applications this year seeking regulatory approval for rolofylline.

The medicine failed to meet the primary or secondary efficacy goals in the 2,033-patient Phase III study among patients with the hard-to-treat condition, in which the heart's pumping ability is not adequate for the body's needs.

Dan Bloomfield, Merck's executive director for cardiovascular research, called the results disappointing, saying that advances for patients with acute heart failure have long been elusive.

Asked whether rolofylline still has a future, Merck spokesman Ronald Rogers said: It would be premature to speculate on that. He said Merck will further analyze the study data and researchers will present it at a medical meeting, where cardiologists can provide feedback.

Then we'll see where we are, Rogers said.

Merck acquired rolofylline in 2007 when it bought NovaCardia. Merck Chief Executive Officer Richard Clark told Reuters in November that rolofylline will be an important drug.

The blow follows several other research setbacks for Merck, which has a long record of producing breakthrough medicines.

The FDA in April 2008 rejected the company's Cordaptive cholesterol pill. Several months later, Merck said it would not resubmit its marketing application for the potential blockbuster product until new safety and efficacy data became available in 2013.

Two months ago some patients taking its experimental treatment for migraine headaches, telcagepant (MK-974), developed possible signs of liver toxicity in mid-stage trials. The company scrapped plans to seek approval for the drug in 2009, while it reviews the product's overall safety.

Meanwhile, Merck's blockbuster Singulair asthma drug has suffered sales declines due to concerns that it raises the risk of suicidal thoughts. And demand has waned for its Gardasil vaccine against the virus that causes cervical cancer, amid difficulty attracting 19- to 26-year old girls and women.

In the midst of the many challenges, Merck hopes to dramatically expand its research pipeline with its planned $41 billion acquisition of Schering-Plough Corp (SGP.N), announced in March. The New Jersey-based drugmakers co-market Vytorin and Zetia, two widely used cholesterol fighters.

Merck is a good research and development company, yet its late-stage pipeline has been uninspiring, and to us its planned acquisition of Schering-Plough is an implicit admission that its internal R&D efforts are not where the company has wanted them to be, Sanford Bernstein analyst Tim Anderson said in a research note.

Even so, Anderson maintained his outperform rating on Merck, saying its best in class research laboratories should ultimately produce important new products.

Merck shares fell 42 cents, or 1.6 percent, to $26.16 in afternoon trading on the New York Stock Exchange. (Reporting by Lewis Krauskopf, editing by Gerald E. McCormick and Derek Caney)

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