As the only side starting the day inside the top six to be in action on Saturday, the Gunners made the most of an opportunity to pull seven points clear at the summit, with Mathieu Flamini also on target.
Jack Wilshere, fresh from his two-goal salvo in the UEFA Champions League against Marseille in midweek, almost got Arsenal off to the perfect start, but saw an early effort crash back off the crossbar.
The breakthrough was to arrive, though, just before the half-hour mark when Mesut Ozil whipped over the perfect cross for Ramsey to get in front of his man and glance into the back of the net, with the Welshman choosing not to celebrate against the club that helped to launch his career.
Cardiff, who have taken points off Everton and Manchester heavyweights United and City on home soil this season, were grateful to Ben Turner for keeping them in the game at the start of the second period, as he blocked an Olivier Giroud shot on the line.
They then came close to drawing level moments later, but Wojciech Szczesny displayed impressive reflexes to get down low and claw away a powerful header from Fraizer Campbell.
Gaps inevitably opened up as the Bluebirds continued to push for parity late on, and Ozil was the man to pick their lock once more as he threaded a pass into the path of substitute Flamini to crash home with aplomb.
Fittingly, Ramsey ensured that it would be he who had the last word in stoppage-time when Theo Walcott squared for him to slide in a third.
Ramsey enjoyed a great reception from the home crowd prior to kick-off, and then almost helped put Arsenal ahead after 70 seconds.
His pass picked out Wilshere, who beat David Marshall with a curling effort which rattled the crossbar.
Arsenal's strong start was punctuated by an injury to Per Mertesacker after the German clashed heads with Bacary Sagna, and Cardiff almost capitalised with the defender on the sidelines having further treatment.
Kevin Theophile-Catherine surged down the right to deliver an inviting cross which Campbell headed wide.
Arsenal should have led in the 15th minute but Giroud made an embarrassing error.
The French striker thought he was offside when Ozil attempted to flick a through ball on to him - with replays suggesting the £42million signing had got a touch - and stopped when clean through on goal, allowing Steven Caulker to get back and put in a block.
Ozil's next contribution saw Arsenal take the lead.
His fizzing cross picked out Ramsey's run and the midfielder's header left Marshall with no chance.
Jordon Mutch sent an attempted overhead kick wide from close range but Arsenal were firmly on top and Ramsey could have doubled their lead just before the break.
Giroud picked him out at the far post but he was crowded out by defenders and eventually sent his shot well over the bar.
Another chance arrived seconds into the second half. Ramsey was again at the centre of it, bursting past Peter Whittingham and Kim Bo-kyung to tee up Giroud, only for Turner to block the goal-bound effort on the line.
The miss almost proved costly when Kim flicked on a ball into the Arsenal box and Campbell rose to direct a powerful header goalwards, only for Szczesny to make an excellent low save.
The chance prompted a big improvement in Cardiff's play, the hosts upping the tempo and finding a way to disrupt Arsenal's passing patterns.
However, they created little and Arsenal remained a potent threat, with Santi Cazorla hitting a tame effort at Marshall from Wilshere's pass.
Whittingham and Don Cowie worked Szczesny from distance before Flamini slotted home from Ozil's pass for his first Arsenal goal since January 2008, and Ramsey added a third in time added on.