A grieving Queens widower who blames cops for not protecting his wife from the stalker who allegedly carved out her heart is suing the NYPD for $15 million.

Yung Wei Guo says he pleaded with police to shield his wife, Qian Wu, 46, from Huang Chen, 47, who allegedly pounded Wu’s head with a hammer 18 times and then stabbed her repeatedly with a utility knife in January 2010.

Just four days before Chen, an illegal immigrant, allegedly killed Wu, the couple spotted him inside their Flushing apartment building, Guo said. They immediately went to the police, obtained their fourth order of protection against Chen and pleaded for additional help, asking that Chen be jailed, he said.

But Chen, who had been stalking the woman since 2006, remained free and wound up ambushing her in the hallway outside the couple’s apartment as she returned home with a gallon of milk.

The city Medical Examiner’s Office discovered that Chen had used the knife to rip Wu’s heart and lungs from her body.

Police officials declined to comment on the pending litigation.