The on-loan Norwich striker broke the deadlock with a composed finish in the 18th minute and was involved in the build-up to Arnaud Djoum’s strike a minute before the interval.
The hosts controlled the game from start to finish and should have added a third but Michael Smith’s penalty, which came shortly after Accies defender Shaun Want picked up his second yellow card in the 71st minute, came back off the crossbar.
Craig Levein’s side were quick out of the blocks and should have opened the scoring inside three minutes.
Callumn Morrison showed neat footwork on the right flank to skip past Scott McMann and his cross towards the far post was headed wide by Scotland striker Naismith despite the goal being at his mercy.
But Naismith was smiling as he gave Hearts the lead 15 minutes later.
Left-back Ben Garuccio found the forward in space and Naismith had time to look up and curl a shot into the corner beyond Gary Woods from 15 yards.
Hearts were dominating and should have doubled their lead after 32 minutes but Steven MacLean shot wide from inside the area after racing on to a quickly-taken Naismith free-kick.
After Hamilton midfielder Scott Martin had a tame effort saved by Colin Doyle, Hearts scored again a minute before the break.
Morrison’s first cross came back to him but his second found Djoum at the back post and the Cameroon international slammed a low right-footed drive into the net.
At 2-0 down, Hamilton began to throw more players forward in the second half but they also became more vulnerable to counter-attacks and Hearts came close to notching a third in the 66th minute.
Substitute Sean Clare broke from a Naismith pass but elected to play in Djoum in the box instead of shooting and Martin got back to make a goal-saving block.
Hamilton’s afternoon went from bad to worse in the 71st minute when Want was shown his second yellow card by referee Don Robertson for pulling on Naismith’s jersey after the striker got on the wrong side of the defender.
Hearts should have added another but Smith’s penalty in the 78th minute came back off the crossbar after Ziggy Gordon was penalised for handball in the area.