Sobhraj, 73, had recently fainted in a special cell of Central Jail of Kathmandu, where he has been kept in confinement for the last 12 years.
After initial check-up, Sobhraj was referred to Shahid Gangalal Hospital on the outskirts of Kathmandu where doctors suggested surgery for the mitral valve leakage.
He was admitted to the hospital today and will undergo open heart surgery on Monday, said a senior doctor at the Central Jail.
The doctor said all the costs required for the treatment will be borne by the Nepal government.
Nicknamed "the Bikini Killer" and "the Serpent" due to his skill at deception and evasion, Sobharaj is serving a life-term in the Kathmandu jail since 2003 for the murder of US woman Connie Joe Bronzich in 1975.
A life-term in Nepal means 20 years in jail. Even if Sobharaj completes the jail term another case is pending in a district court of Nepal to convict him.
He had been linked to multiple killings of backpackers.
Sobhraj spent 21 years in jail in India with a brief 22day break in 1986 when he escaped Tihar Jail after drugging security guards, whom he had served sweets on the pretext of celebrating his birthday.
Sobhraj is believed to have killed 15 to 20 people in 1970s. Two of his victims were found wearing only bikinis. He befriended mostly Western tourists in Asia, later drugging and killing them mostly between 1972 and 1976.