The 62-year-old BJP MP had collapsed during a meeting chaired by party president Amit Shah at Jaipur last week, following which he was admitted to the ICU of Sawai Man Singh Hospital there.
"His condition is critical. He is on ventilator," AIIMS Director Randeep Guleria said.
The saffron leader was airlifted to the All India Institute of Medical Sciences (AIIMS) on Thursday.
According to the doctors at AIIMS, Jat had a cardiac arrest which has caused damage to his brain.
A team of doctors is monitoring his condition.