Doctors said that Mr Sharon, comatose since suffering a stroke in January, had been moved to intensive care when the infection threatened his heart function.
The hospital said doctors treated the infection and transferred Mr Sharon back to the respiratory ward, where he has been hospitalised since being moved to Sheba in May.
He has undergone several extensive brain operations to stop cerebral haemorrhaging, in addition to several minor procedures.
Mr Sharon lapsed into a coma just months after he ended Israel's 38-year occupation of the Gaza Strip and bolted his hard-line Likud Party to form the centrist Kadima faction.
After the stroke, Mr Sharon's successor, Ehud Olmert, led Kadima to victory in a March 28 vote and became prime minister.