A large study of an alternative treatment for heart-attack survivors has stopped enrolling new patients while federal officials investigate whether participants were fully informed of the risks, the Associated Press reported.

The study seeks to determine whether a controversial treatment called chelation, which has mainly been used to treat lead poisoning, is also safe and effective for heart patients. The physician who is leading the study, Gervasio Lamas of the University of Miami, told the news agency that he believes the study is “safe and ethical” and that its patients are protected.

The federal Office for Human Research Protections began investigating the study after another physician, Kimball Atwood, an anesthesiologist in suburban Boston, and other critics raised questions about whether participants had been adequately informed of dangers associated with the treatment and whether some doctors involved in the study had financial conflicts of interest.

People already enrolled are still being treated, said a spokeswoman for the National Heart, Lung, and Blood Institute, which is sponsoring the study with the National Center for Complementary and Alternative Medicine. —Charles Huckabee