Judge Rajalakshmi also slapped a fine of Rs 3 lakh on each of them.
According to the prosecution, the Narcotics Intelligence Bureau got a tip-off that there was a plan to smuggle heroin worth several crores of rupees from Tiruchendur coast in Tuticorin to Sri Lanka, and it kept a close watch on the coastal area on January 7, 2006.
They arrested A Thangadurai and C Mariya Siluvai, who were moving around suspiciously and seized 4.170 gm heroin worth Rs 4.17 crore from them.
The judge said it had been proved that the duo had smuggled the narcotics and sentenced them under the NDPS Act.