Bulgarian customs officials seized 403 kilograms of heroin, valued at 8.5 million euros, in a Turkish-registered truck traveling from Iran to Western Europe.
The heroin was in 618 packages hidden in 156 mattresses that the truck was officially transporting, writes AP.
The prosecution statement states that the heroin shipment was seized at the Kapitan Andeevo border crossing with Turkey.
The drug is believed to have originated in Iran and was destined for sale in other EU member states.
The driver of the Turkish truck was arrested and faces 20 years in prison if convicted of drug smuggling.
Bulgaria, which is on the drug route from the Middle East to Western Europe, has taken extensive measures in recent years to prevent drug smuggling.