Health Canada is alerting consumers who take Losec and Nexium, two prescription medications primarily used to treat acid-related stomach disorders, that it is investigating the drugs' links to serious cardiac problems.

Studies of the two medications reveal that patients using Losec or Nexium to treat gastroesophageal reflux disease (GERD) instead of surgery "may have experienced more heart attacks or cardiac deaths than patients who had the surgery," reads the advisory.

It also notes that many patients who developed cardiac problems had risk factors prior to beginning treatment.

The data being reviewed by Health Canada comes from a study that compares treatment with Losec to surgery in patients with severe GERD. Another continuing study comparing Nexium to surgery has five-year followup information on patients.

The study designs did not provide for a clear definition of cardiac problems or an adequate followup of patients. While both studies include some safety data, Health Canada said it is difficult to evaluate this data because of the way it was collected, reported and documented.

At this point, Health Canada's preliminary review finds the evidence provided does not confirm the existence of a possible cardiovascular risk. It plans to complete its analysis of the new information by the end of the year and will advise Canadians of its conclusions and recommendations at that time.

Health Canada is advising health professionals not to change their prescribing practices of the drugs for the time being.

Patients taking Losec or Nexium are also urged to consult with their doctors before making any change to their medication, as GERD can lead to other complications if left untreated.

Any adverse reactions to either drug should be reported to the Canadian Adverse Drug Reaction Monitoring Program, said Health Canada.