Former Prime Minister Dr Manmohan Singh was admitted to All India Institute of Medical Sciences (AIIMS) on Sunday following chest pain.
"Former Prime Minister Dr Manmohan Singh has been admitted to AIIMS after complaining about chest pain," hospital officials said.
The 87-year-old veteran Congress leader was taken to the AIIMS cardio-thoracic ward and is currently under observation.
In 2009, Singh underwent heart-bypass surgery at AIIMS, in which five grafts -- channels to bypass blocked arteries -- were implanted in surgery.
He currently represents Rajasthan in the Upper House of Parliament. He served as the prime minister between 2004 and 2014.
( With inputs from ANI )