Details of a large heart safety study presented on Monday appear to give Merck and Co's diabetes drug Januvia a clean bill of health, possibly setting the stage for a return to sales growth for the drugmaker's biggest product. Merck in April said the study, called Tecos, of 14,724 patients with type 2 diabetes and a history of heart disease demonstrated that adding Januvia to usual care did not increase major heart problems any more than adding a placebo, removing a cloud that has been holding back sales of the medicine and the company's share price.