Senior Congress leader P Chidambaram fell unconscious at the Sabarmati Ashram in Ahmedabad on Tuesday and was taken to hospital.
Sources said he probably fainted due to the heat after a hectic day.
The 79-year-old former finance minister's son Karti later said on X that his father is fine and is being examined by doctors.
The incident occurred when Congress leaders were attending a prayer meeting at the Sabarmati Ashram.
As Chidambaram fell unconscious, he was carried by other leaders to an ambulance which took him to hospital.
Earlier in the day, Chidambaram attended the extended Congress Working Committee meeting at the Sardar Vallabhbhai Patel National Memorial.