"They were seated at a table with Serena Williams and couldn't stop kissing [at 1OAK in West Hollywood last week]," says our source. "They were still there when the lights came on at 2 a.m., and that's when Heidi grabbed Vito's hand and they walked toward the exit."

They two were first linked in February, when they were seen leaving Hollywood club Bootsy Bellows together. Until Oscars week, the beauty and the bohemian had tried keeping things on the down-low.

"They are really into each other -- this isn't a fling," said a friend of the couple. "Heidi wanted Vito to be in L.A. this week with her."