Paul Pelosi, the husband of House Speaker Nancy Pelosi, was "violently assaulted" after a break-in at the couple's California home early on Friday, her office said.
In a statement, her office said: "The assailant is in custody and the motivation for the attack is under investigation.
"Mr Pelosi was taken to the hospital, where he is receiving excellent medical care and is expected to make a full recovery.
Nancy Pelosi
KEVIN LAMARQUE
Nancy Pelosi and Paul Pelosi
KEN CEDENO
"The Speaker was not in San Francisco at the time."
Ms Pelosi, who is second in line to the US presidency, was not at home at the time of the early morning break-in.
The circumstances of the attack were unclear, including how the intruder got into the home.
The assault comes less than two weeks before midterm elections in which control of the House and the Senate is at stake.
Mr Pelosi, 82, who owns a San Francisco-based real estate and venture capital firm, was convicted of a misdemeanour charge of driving under the influence of alcohol after becoming involved in an auto accident in May.
He was sentenced to five days in jail in Napa County, California.
