The Smithsonian’s National Museum of American History has named David Allison, associate director of curatorial affairs, as acting director, said a museum spokeswoman.

The appointment came after Director John Gray, who had headed the museum since July, had a heart attack Tuesday morning and was taken to George Washington University Hospital, where he was reported in stable condition as of Friday evening.

Richard Kurin, the Smithsonian’s undersecretary for history, art and culture, asked Allison to step in as acting director Tuesday afternoon, museum spokeswoman Melinda Machado said. She said there was no information yet about how long Allison would be asked to serve in this position.

Gray, 64, who had been president of the Autry National Center of the American West until late 2010, came out of retirement to lead the Smithsonian’s third most popular museum, overseeing a collection of more 3 million objects.

In a May interview, Gray told The Washington Post: “There is no more important American history museum than this one, and no other has more responsibilities than this one.”