"As scientists, we're excited about this discovery because it's a fundamentally new approach to regulating what enzymes do in cells," said Queens University Professor Donald Maurice, who led the study. "The fact that it also offers a potentially novel use of a drug already widely in use for other applications is an unexpected bonus."

The enzyme, PDE5, is known to regulate the activity of platelets: small blood cells needed for normal blood clotting. Problems can arise when people have stents permanently implanted in their arteries to maintain blood flow. Their platelets sometimes bind to the stent and, if enough platelets accumulate to form a blockage, this may cause a heart attack or stroke.

Viagra has been shown to inhibit PDE5, said Lindsay Wilson, graduate student and first author of the study. "The idea is to use a PDE5 inhibitor such as Viagra to selectively inhibit platelet function," Wilson added.

The study appears in the online early edition of the Proceedings of the National Academy of Sciences.