PMK founder-leader Dr S Ramadoss hospitalised since his release on bail last week after 12-day imprisonment underwent heart surgery on Monday at a corporate hospital in Chennai.
The surgery was performed on Monday morning. The 75-year-old was keeping "well" and will be in the Critical Care Unit (CCU) for the next three days, party sources said.
Mr Ramadoss was arrested on April 30 for trying to stage a protest at Villupuram, defying a ban seeking arrest of culprits behind the April 25 Marakkanam violence.
He was admitted to the hospital as he complained of breathlessness after being released from Tiruchirappalli central prison on May 11 on being granted bail.
The Marakkanam violence was allegedly targeted at Dalits, and Chief Minister J Jayalalithaa had blamed PMK for the incident. But the PMK has denied its involvement.
Mr Ramadoss was arrested in connection with four other cases also but was granted bail in all of them.
His arrest triggered widespread violence in several parts of the state, leading to the detention of a large number of party workers, including several under the stringent Goondas Act and National Security Act.