A Mexican man in Border Patrol custody died Monday of a pre-existing heart condition, U.S. Customs and Border Protection (CBP) said in a Tuesday statement.

The 49-year-old man, who has not been identified, was apprehended Sunday afternoon by Tucson Sector Border Patrol agents, who determined he needed immediate medical attention.

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The Mexican national was taken to a hospital in the Tucson area, where he died Monday morning.

"U.S. Customs and Border Protection is saddened to report a 49-year-old man from Mexico was pronounced deceased Monday morning in a Southern Arizona hospital. Our condolences are with his family," wrote CBP officials in the statement.

The man was the second immigration detainee to die this month.

The first was a Cameroonian national, 37-year-old Nebane Abienwi, who died Oct. 1 under Immigration and Customs Enforcement (ICE) custody in a Chula Vista, Calif., hospital.