Jeffrey Dean Morgan returns to <EM>Grey's Anatomy.</EM> Jeffrey Dean Morgan returns to Grey's Anatomy.

Izzie is so over Alex. That's because Katherine Heigl's sweet intern finds love on Grey's Anatomy (Sundays at 10 pm/ET) with returning heart-transplant patient Denny Duquette (played by Jeffrey Dean Morgan) instead. Well, at least for a nine-episode arc chronicling Denny's quest for two hearts  Izzie's and a new one for himself.

"I'm there to shake things up a little bit," Morgan says. His wealthy marine-biologist character departed on the Jan. 15 episode without a desperately needed transplant. Disappointed, Izzie thought that was goodbye.

Grey's Anatomy fans won't see Denny for at least a few episodes, but when he does return, Morgan promises pulses will quicken. "Izzie [gives him] a whole new reason to live," says Morgan, whose character believes it was love at first sight with the beautiful doctor. "It's going to be really interesting how it plays out. There's great chemistry."

One doctor who doesn't appreciate their chemistry is Alex Karev (Justin Chambers), Izzie's ex-squeeze. "I would anticipate confrontation," Morgan says. "Denny isn't going anywhere, and Alex isn't going anywhere.... Neither of them wants to let Izzie go."

Fighting for Izzie's heart is keeping Morgan a very busy man. In addition to his role on Grey's, he plays the phantom-fighting father on WB's Supernatural and Mary-Louise Parker's deceased husband (who appears in flashbacks and dream sequences) on Showtime's comedy series Weeds.

Shooting Grey's Anatomy in Los Angeles and Supernatural in Canada doesn't leave much time for Morgan's off-screen romance with actress Sarah Lancaster (she was Ephram Brown's love interest, Madison Kellner, on Everwood). "It's tough right now," he says. "The minutes I use on my text [messages]! Lots of I-love-you's back and forth." But the actor is grateful for the opportunity to return to Grey's Anatomy. "I can't remember ever being on a show where everyone is so damn happy to be back," he says. "The atmosphere is amazing."