The United States Army is investigating whether certain dietary supplements for athletes, available until recently at stores on military bases in the United States, may have played a role in the deaths of two soldiers.

Both soldiers died last year after having heart attacks during fitness exercises, according to a spokesman for the Army’s assistant secretary of defense for health affairs.

With names like Jack3d and OxyElite Pro, these supplements are popular with athletes because they contain an ingredient, known as dimethylamylamine or DMAA, advertised to increase energy, concentration and metabolism. The products are best sellers among fitness buffs at stores like GNC and the Vitamin Shoppe, as well as on Web sites like bodybuilding.com.

As a precaution, the Defense Department has removed all products containing DMAA from stores on military bases, including more than 100 GNC shops, pending the completion of an Army safety review, said Peter J. Graves, an Army spokesman.