Mariah Carey shows off 18 carat yellow heart shaped diamond necklace worth $500,000

Mariah Carey�s billionaire's boyfriend James Packer put $500,000 worth of rocks on her chest on Thursday before her performance. Packer gave Mariah an 18 karat yellow heart-shaped diamond, which he gave to her right before she went on stage for her Vegas show at Caesars Palace. She gave a shout out to him after her performance.

Mariah Carey thanked JP for "a new heart" ... right before she sang "Hero" that night.

She told the audience: 'I have a new heart tonight' as the crowd whooped and cheered.

Mariah continued: 'James is in my heart tonight.' 

Before she went on stage Mariah took a shot of herself in her new jewels and posted it on Thursday morning.

She captioned it: 'Happy backstage right before last night�s show...#NTT ��If you look inside your heart.'