Bristol-Myers Squibb Co and Pfizer Inc could provide new data within days on an experimental blood thinner, revealing its potential in a highly lucrative market for millions of patients with dangerously irregular heart rhythms. Their pill, apixaban, if approved, will likely be the third entrant among a new crop of oral anti-coagulants meant to replace warfarin, the current standard for preventing stroke among patients with atrial fibrillation. Each of the medicines has the potential for topping $2 billion in annual sales. Even if late to market, apixaban could catch up with rival newcomers thanks to Bristol-Myers' and Pfizer's vast sales networks for cardiovascular treatments -- but only if data from the highly-awaited Phase III trial measure up.