The country's ex-military ruler felt unwell while he was heading to a hearing in his treason case under heavy security, police said.

The 70-year-old man had been summoned to the special tribunal in Islamabad after failing to show up for two previous sessions due to security threats against him.

Police officers stand guard at the gate of the Special Court in Islamabad

Jan Mohammad, a senior police official, told the court: "He has been shifted to Armed Forces Institute of Cardiology (in the nearby city of Rawalpindi) after he got heart problem."

An aide to Mr Musharraf, who is facing a series of criminal cases dating back to his 1999-2008 rule, said the retired general was in "bad shape".

Meanwhile, his lawyers walked out of court, complaining they were being threatened and harassed by the government.

Anwar Mansoor Khan, one of the lawyers, told the court he had been unable to sleep the previous night due to someone banging on his door.

Musharraf is accused over the death of former prime minister Benazir Bhutto

"I was under total threat," he told the court. "From 1am to five in the morning. Someone was banging on my door and ringing my bell."

When asked who was threatening him, Mr Khan answered: "This very government."

"This never happened in my 40 years of practice. I will walk out," Mr Khan said; which he did.

He had earlier told the court he had been attacked in his car while travelling to the eastern city of Lahore following a hearing.

Mr Musharraf's lawyers have previously claimed the treason case is an attempt by the government of Prime Minister Nawaz Sharif, whom Mr Musharraf ousted in a coup in 1999, to settle old scores through the courts.

The treason allegations follow a series of criminal cases faced by Mr Musharraf since he returned to Pakistan in a failed bid to run in last May's general election.

The charges include murder, over the assassination of former prime minister Benazir Bhutto in 2007.

Mr Musharraf appeared briefly in court in August 2013 were he denied the charges.