Bayer A.G.’s limp excuse for withholding data suggesting that a heart-surgery drug is dangerous won’t wash. The failure by the German pharmaceutical giant to inform the Food and Drug Administration of the disquieting results of a large observational study cannot be sloughed off as a mere “mistake on the company’s part.”

Rather, the circumstances suggest that Bayer sought to hide the results of a contractor’s study until some way could be found to discount them. It came clean only when forced to by a whistleblower.

The drug is Trasylol, which has long been used in heart surgery to reduce blood loss and the need for transfusions. Although extensive data seemed to document the drug’s effectiveness and safety, two studies published this year found that it increased the risk of kidney failure, heart attack and stroke.

Even so, an F.D.A. advisory committee, after reviewing extensive data at a public meeting on Sept. 21, overwhelmingly concluded that Trasylol was still acceptably safe and effective for certain patients. The committee had not been told — because Bayer representatives who participated in the meeting kept mum — about the most recent large study the company had sponsored, which raised even more questions about the drug’s safety.

After the fact, a whistleblower, possibly an outside researcher, reportedly called both the F.D.A. and Bayer to force full disclosure. Preliminary results of the suppressed study showed that Trasylol may increase the chance for death, serious kidney disease, congestive heart failure and strokes.

The company says it did not initially disclose this retrospective study of some 67,000 patients because it deemed the results preliminary and had significant questions about the methodology and populations of patients. That may be. But that cannot be an excuse for hiding the very existence of this study from an expert advisory panel convened to review the latest safety evidence.

This incident underscores the importance of requiring drug companies to publicly register all safety studies so that they can’t be suppressed later should their results displease the sponsor.