The 85-year-old leader was admitted to the hospital in the morning and is undergoing treatment, the doctors attending on him said.
According to DMK sources, Karunanidhi also complained of severe back pain.
Karunanidhi, who underwent a major surgery for his back problem in February, had hit the campaign trail for the Lok Sabha elections only two days ago.
Karunanidhi has successful back surgery
Karunanidhi calls off fast over Lankan Tamils
Complete coverage: India Votes 2009