A heartless thug who mugged a grandmother — snatching a gold crucifix from the 87-year-old East Harlem woman — glowered yesterday as he was marched off to serve three years in prison.

Feisty victim Margarita Fuentes, who has 17 grand and great-grandchildren, had picked crackhead Arnel Muñoz out of a lineup.

“He left me there bleeding. I went to the hospital. I feel better knowing he’s behind bars,” Fuentes said. “He did the crime, and now he needs to pay.”