The U.S. Food and Drug Administration (FDA) has announced that two nuclear stress test drugs, those being ones administered independently of physical examination, should be closely monitored for their risks of heart attack and death.

The FDA advised doctors and health care professionals that Lexiscan (regadenoson) and Adenoscan (adenosine), two stress test drugs that help identify coronary artery disease, may cause fatal heart attacks in patients due to the way the two drugs reduce the flow of certain arteries as they improve the flow in others. Patients who cannot exercise adequately for traditional stress tests must take artery-dilating drugs so doctors can observe the flow of blood to the heart. But this reduced flow can seriously affect obstructed arteries, resulting in a heart attack, so the agency has updated all warning labels to reflect the risk.

Before taking the two drugs, patients should be aware of any “signs or symptoms of unstable angina or cardiovascular instability, as these patients may be at greater risk for serious cardiovascular adverse reactions,” the FDA stated in a news release.

Prior warning labels advised consumers about the risk of heart attack and death. "However, recent reports of serious adverse events in the FDA Adverse Event Reporting System database and the medical literature prompted us to approve changes to the drug labels to include updated recommendations for use,” the agency explained.

The risk of heart attack and death is rare, the agency says, but the threat is serious, so any decision to take either Lexiscan or Adenoscan should first be discussed with a doctor. Heart attacks — known formally as myocardial infarction — occur as a result of restricted blood flow to the organ. The shortage of blood deprives the heart of oxygen, injuring the muscles that enable it to pump.

Stress tests are normally administered only when patients report chest pain or their doctor detects an increased risk for heart disease. While many examinations require patients to perform a series of baseline physical tests, such as running tests of endurance, some patients cannot perform such functional movements. In these cases, doctors often result to more direct means of assessing heart health, in the form of induced hyperemia — or increased blood flow in certain tissues around the body.

The FDA says it’s currently unable to discern whether Lexiscan and Adenoscan pose varying risk for heart attack and death.