"The surgery began on Wednesday morning," a spokesperson for the Asian Heart Institute, located in suburban Bandra Kurla complex, said.
The former Bihar chief minister has been diagnosed with 'aortic stenosis'. Asian Heart Institute Medical Director Vijay D'Silva had said on Tuesday that the surgical procedure will take over five hours.
Institute head Dr Ramakanta Panda, who had operated on former Prime Minister Manmohan Singh five years ago, said the decision to perform the surgery followed a series of medical tests and evaluation on the 66-year-old leader, who was admitted to the institute on Monday.
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