The 72-year-old ex-commando-turned-politician was admitted to the Pakistan Navy Ship Shifa or PNS Shifa, a multi-speciality naval medical treatment facility.
Sources said Musharraf was sitting with family at his home in Karachi - where he lives with his daughter to seek medical treatment for a spinal condition - when he fainted.
He was rushed to the hospital amid tight security and his situation is being monitored. His personal physicians have also been called to the hospital.
"There is nothing serious with him as it was only high blood pressure. He is getting treatment in hospital," Ishaq said.
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Last month, Musharraf was acquitted by an anti-terrorism court in the 2006 murder case of Baloch nationalist leader Nawab Akbar Khan Bugti, the first major relief to the ex-military ruler entangled in several high-profile cases.
He came to power in a bloodless coup in 1999, deposing then-prime minister Nawaz Sharif. Facing impeachment following elections in 2008, Musharraf resigned as president and went into self-imposed exile in Dubai.
He is also facing trial in high treason case for abrogating the constitution in 2007 and illegal detention of judges same year. In January, 2014, Musharraf suffered a "severe heart attack" on his way to a special court to face the high treason charges following which he was admitted to an army hospital.
Musharraf has also been charged in connection with the 2007 assassination of prime minister Benazir Bhutto and the killing of a radical cleric in Islamabad in a military crackdown.