Pfizer, the largest pharmaceutical company in the world, has stopped development of its most promising drug.  The move has rocked both the medical world and the stock markets. 

Cardiologists hoped it would revolutionize heart medicine.  Dr. Steven Nissen led one of the earlier studies of torcetrapib. "I had great hopes for this drug.  I thought we could make a difference with it.  I thought it was going to work.  It didn't."

Pfizer was hoping torceptrapib would reduce the buildup of plaque in blood vessels that can cause heart attacks. 

The drug was also designed to raise the body's good cholesterol, or HDL, by about 50 percent. 

Pfizer stopped the drug's final clinical test because 82 people taking it died during the trial, compared to 52 in the control group not taking the drug.

When this information came in, Pfizer stopped the trials and announced it was abandoning the most promising drug it was developing -- promising both medically and financially, promising that is, until the unexpectedly high number of deaths.

Cardiologist Christopher Cannon expresses concern about the risk. "The higher mortality rate may be small in numbers of patients, but when we think about the tens of millions of people with heart disease who could potentially be treated by this drug, that turns into a large number of patients who could be at risk."

Another pharmaceutical company, AstraZeneca, produces a rival cholesterol drug called Crestor, already on the market.

Roche, another firm, has a drug similar to torcetrapib, still being developed.