Eduardo scored a brace almost a year after breaking his leg to help Arsenal cruise past a lacklustre Cardiff in their FA Cup fourth-round replay.
The Croatia striker missed a header and a cheeky lob before grabbing the opener, nodding in Carlos Vela's cross.
Nicklas Bendtner doubled the lead when he headed in Samir Nasri's corner, before Eduardo scored from the spot after he was felled by Gavin Rae.
Robin Van Persie fired a fourth past the impressive goalkeeper Tom Heaton.
The Gunners will now face Burnley at the Emirates on the weekend of 7/8 March with the winner of that tie at home to Sheffield United or Hull in the quarter-finals.
It was three weeks since Cardiff produced a fantastic display to hold Arsenal to a goalless draw at Ninian Park, but despite being undefeated in 13 league and cup games before tonight, they lacked composure and belief in all departments on Monday.
With the Gunners unbeaten in 11 games but having scored only once in four games before Monday night's tie, manager Arsene Wenger will have been delighted to see striker Eduardo in action again.
The 25-year-old Brazil-born Croat made his long-awaited first-team comeback after fracturing his left fibula and dislocating his ankle in a tackle by Birmingham's Martin Taylor in February 2008.
The hosts were in full flow from the first whistle and came close to scoring three times in the opening eight minutes.
An unmarked Bendtner headed a Bacary Sagna cross narrowly wide and then Cardiff had their keeper Heaton - on loan from Manchester United and playing in place of Peter Enckelman - to thank for thwarting the rampant Arsenal attack.
Heaton palmed away a Vela pile-driver from 30 yards, before saving the follow-up from Bendtner. One minute later the keeper's gloves were in action again as they pushed away a William Gallas header.
After a missed header and a cheeky lob from the halfway line, Eduardo grabbed the opener on 19 minutes when he started and finished a fine move.
Eduardo poked the ball through to Vela, a real menace down the left throughout, who crossed into the box for his Brazilian-born team-mate to nod into the top corner.
Nasri almost doubled the lead after steaming through to the edge of the box and firing in a swerving shot that Heaton nearly mis-read but was eventually able to smother.
The Emirates crowd did not have to wait long for the second. An in-swinging corner from Nasri found Bendtner rising at the front post and he glanced his header inside the far post.
It was a miracle last year's FA Cup runners-up were not three behind at the interval with Bendtner guilty of a shocking miss.
Seconds after Heaton denied Vela, the ball fell to Bendtner but he could only hit the post.
He still had a chance to tuck in the rebound but Heaton heroically denied him.
Lukasz Fabianski had his first work to do in the Arsenal goal just before the hour after comfortably saving a 25-yard blast from Jay Bothroyd.
Two minutes later Eduardo was celebrating his team's third, converting a penalty he himself had earned after being clumsily bundled over by Rae. Eduardo's ensuing hugs with the Arsenal medical staff was a touching moment.
Eduardo's efforts were rewarded with an early breather 25 minutes from the end and he was replaced by Van Persie.
Apart from a free-kick by top scorer Ross McCormack which was deflected over the bar, Cardiff continued to be devoid of ideas and manager Dave Jones threw on Darcy Blake, Peter Whittingham and Riccardo Scimeca to inject some creativity.
Van Persie completed the demolition two minutes from the end, blasting in from the edge of the box after a pass from Bendtner, and the Dutchman headed against the post in the final action of the game.
Arsenal boss Arsene Wenger on Eduardo:
"He had a good game for his first game back. When you have such a long time out, it's difficult to be patient, to come in every day and see everyone else play. He had to deal with a lot of frustrations.
"I believe - as any striker - he can contribute and help us to win games. He has the perfect spirit, he is talented and is intelligent."
Cardiff manager Dave Jones on their display:
"The basics of the game - what we're normally good at - we didn't do today and it's hard. Sometimes you've just got to stand there and you've got to swallow that.
"The players know that we didn't perform anywhere near what we're capable of. So we now have to forget this one, let it eat away at us and then get concentrating on the job in hand.
"It wasn't the Cardiff we've seen all season... I know we're playing Arsenal and everything else - full credit to them - but we didn't do ourselves any justice."
Arsenal: Fabianski, Sagna, Toure, Gallas, Gibbs, Nasri (Ramsey 67), Denilson, Song Billong, Vela (Bischoff 74), Eduardo (Van Persie 67), Bendtner.
Subs Not Used: Almunia, Wilshere, Clichy.
Booked: Gallas, Bendtner.
Goals: Eduardo 20, Bendtner 34, Eduardo 60 pen, Van Persie 89.
Cardiff: Heaton, McNaughton, Purse (Blake 68), Roger Johnson, Kennedy, Burke, Rae (Scimeca 74), Ledley, Parry (Whittingham 68), Bothroyd, McCormack.
Subs Not Used: Sak, Capaldi, Eddie Johnson, Comminges.
Ref: Mark Halsey (Lancashire).