The Palestinian prime minister, Salam Fayyad, suffered a heart attack on Sunday at a hospital in Austin, Tex., where he was attending his son’s college graduation, a spokesman said. Mr. Fayyad, a heavy smoker, underwent tests showing a blockage in a coronary artery, and doctors performed a catheterization to open the artery, the spokesman said. He is expected to leave the hospital in two days. Mr. Fayyad has been prime minister since 2007 and has developed close ties with Western leaders.