A stress test on a treadmill is the common way to diagnose coronary artery disease, but each year as many as a half-million Americans who are at risk cannot take the test because of lung disease, obesity, or frailty. The alternative has been angiography, a costly cardiac catheterization procedure. In early February, Du Pont Merck Pharmaceutical Co. will offer a new drug, IV Persantine, which simulates some of the effects of exercise--dilated arteries and increased blood flow--without forcing the patient onto the treadmill.

Patients would take the drug intravenously along with the radioactive thallium used in some stress tests. While it may not be suitable for those who have just had heart attacks or who have severe asthma, it's expected to find wide use. Du Pont Merck is licensing the drug, which has long been used to treat complications of heart valve replacements, from Boehringer Ingelheim International of Germany.

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