Former Malaysian Prime Minister Mahathir Mohamad underwent surgery and was back on a respirator on Sunday after a recent heart bypass led to a chest infection, a hospital statement said. Mahathir, 82, who ruled for 22 years until 2003, went back into the operating theatre at Kuala Lumpur’s National Heart Institute around midnight on Saturday to have infected tissue cut out of his chest, an aide to the former premier added. “He is on full support,” the aide said, adding that Mahathir was still not conscious and was breathing with the support of a respirator in the institute’s intensive-care unit.