The 82-year-old suffered blunt force injuries in the attack, according to two sources.
Earlier, Ms Pelosi’s spokesman said her husband was expected to make a full recovery. She was not at home when the attack took place.
Spokesman Drew Hammill said the alleged assailant is in custody and the motive for the attack is under investigation.
“The speaker and her family are grateful to the first responders and medical professionals involved, and request privacy at this time,” Mr Hammill said in a statement.
Ms Pelosi just returned to Washington this week from a security conference in Europe and is due to deliver a keynote address at an advocacy event on Saturday evening with US vice president Kamala Harris.
While the circumstances of the attack are unclear, the incident raises additional questions about the safety of members of US congress and their families as threats to legislators are at an all-time high almost two years after the violent Capitol insurrection.
Members of congress have received additional dollars for security at their homes, but some have pushed for more protection as people have showed up at their homes, with members receiving an increasing amount of threatening communications.
Often at Ms Pelosi’s side during formal events in Washington, Paul Pelosi is a wealthy investor who largely remains on the West Coast. They have five adult children and many grandchildren.
Earlier this year, Mr Pelosi pleaded guilty to misdemeanour driving under the influence charges related to a May crash in California’s wine country and was sentenced to five days in jail and three years of probation.
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