The breakthrough drug Gleevec, which has been proven to stop the progress of CML: Chronic Myelogenous Leukemia, has now been found to possibly lead to congestive heart failure in some patients.

A study released by the Journal Nature was prompted after reports indicated that 10 patients on Gleevec developed severe heart failure. Officials and doctors in Connecticut say although this is a side effect of the drug, the negative does not outweigh the positive.

Novartis, the drug's maker, says this is a very rare side effect, but has placed a warning on the drug's label.