Experimental blood substitutes raised the risk of heart attack and death in people who were given them – but U.S. regulators allowed human testing to continue, says a scathing new report.

The U.S. Food and Drug Administration fell short, the report contends, even as red flags popped up during studies by five biotech companies. Rules barred the agency from releasing company trade secrets, and that kept some information hidden and may have led to unnecessary heart attacks and deaths, wrote the authors.

One of the studies reviewed in the report, using the blood substitute PolyHeme, was conducted at sites including Kansas University Hospital and included patients in Douglas and Leavenworth counties. Dr. Michael Moncure, the lead researcher for the project at KU Hospital, said that in the trauma study, which was conducted at several other sites as well, 11 of 350 patients who received PolyHeme had heart attacks. None of the patients in the control group had heart attacks.

“If we knew then what we know now, we would obviously be a lot more cautious,” Moncure said. “Up to then, there were not studies that showed any propensity toward death or heart attack.”

Moncure added that while there were more heart attacks it wasn’t enough to be statistically significant. He added that patients who received PolyHeme had no better clinical response than those who received traditional treatment with saline and normal blood.

The trials were controversial at the time because they involved treating patients experimentally even though they usually were unconscious at the time.