Zaidi was arrested on August 29 and remanded to 14 days judicial custody on September 7.
He is lodged in Kanda jail.
A team of doctors conducted his medical examination and he has been admitted in the Cardiac Care Unit (CCU), police said.
Zaidi had headed the Special Investigation Team (SIT) constituted by the Himachal Pradesh Police to probe the July 4 rape and murder of a school girl in Kotkhai area. He along with seven other police officials was arrested by the CBI in connection with the custodial death of Suraj Singh, one of the six accused in the case.