A federal judge in Laredo on Monday accepted guilty pleas from 36-year-old Norma Alicia Flores-Recio and 44-year-old Oscar Segura.
Guards intercepted three cards that contained drugs.
Flores-Recio pleaded guilty to providing heroin to Segura when he was an inmate in the Webb County Jail. He pleaded guilty to attempting to obtain heroin while jailed.
Both remain in custody pending sentencing. Further details were not immediately available on when and why Segura was originally jailed.