Agents with the U.S. Customs and Border Protection arrested an American woman Saturday after she attempted to cross the border with $1.5 million worth of heroin.

The narcotics were found concealed in a Volkswagen Jetta.

CBP officers encountered the 28-year-old U.S. citizen from Edinburg, Texas, arriving from Mexico at the Pharr-Reynosa International Bridge, according to a press release.

When the woman entered the border crossing area at the bridge, authorities determined the car needed a “more thorough examination.”

CBP officers “discovered that the car’s tires contained suspected narcotics,” the press release stated.

A canine team assisted with the inspection of the car and discovered packages of heroin hidden in the tires. The packages weighed roughly 55 pounds and are estimated to be worth $1.5 million.

The officers seized the vehicle and the narcotics. The woman was arrested and turned over “to the custody of agents with Homeland Security Investigations (HSI) as they continue with the investigation.”

Authorities have not released her name.