He may not be getting much sleep these days, but Patrick Dempsey is having a ton of fun with fatherhood - and filming Season Four of Grey's Anatomy.

The actor tells Extra that his 6-month-old twin sons, Darby and Sullivan, "are developing beautifully ... It's a lot of fun."

It's a sentiment he echoes when asked about filming the latest installment of his hit TV show: "It's a lot lighter, people are having more fun."

"The energy and the adjustments make a big difference," he says.

Last year, on-set turmoil that finally led to the departure of Isaiah Washington cast a pall over much of the season.

Regardless of how people feel about that incident, fans will surely echo Dempsey's sentiment about moving on and getting back to business.

Definitely pumped to be back at Seattle Grace, Patrick declared to Extra, "I'm just excited to go save some lives again!"

Patrick Dempsey, 41, who races cars on the Hyper Sport racing team, plans to have the twins (and daughter Talula, 5) driving "soon enough."

"You can get those little go carts," he says, smiling, but adds that there'll be "no pressure" for them to race like dad.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.