Heatley, who recorded a hat trick against the Panthers last week in a 6-4 victory at Florida, scored an early power-play goal then added his second before the first period was halfway over.
Andrej Meszaros and Chris Kelly each had a goal and an assist and Mike Fisher, with a shorthanded goal, and Antoine Vermette also scored for Ottawa (13-12-1), which took advantage of an horrendous defensive outing by Florida.
The Senators chased Panthers starter Alex Auld from the net after the goaltender gave up five goals on 17 shots in little more than 26 minutes of work before a crowd of 17,814 at Scotiabank Place.
At the other end, Ray Emery, getting the start at home ahead of the inconsistent Martin Gerber, was solid in stopping 31 shots to record his first shutout of the season and fourth of his career.
Ottawa has now won six of its past seven games and is above the .500 mark for the first time since it was 5-4-0 on Oct. 26.
The Panthers, meanwhile, are headed in the exact opposite direction. They followed up their first loss to Ottawa last Friday with back-to-back 1-0 losses to Atlanta and Montreal, respectively and have now gone 201 minutes, 21 seconds without a goal.
The loss was Florida's fifth straight and sixth in the past seven games, dropping the Panthers (8-14-5) to just 2-8-4 on the road. They have been outscored 48-22 away from home.
Ottawa defenceman Wade Redden, who has been in and out of the lineup this season with groin problems, left the game with an upper-body injury and didn't return after taking a hit late in the first period. His status was not immediately known.
Panthers blue-liner Mike Van Ryn took a shot off his right leg while killing a penalty in the third period and left the game. His status was also not known.
Heatley put the Senators in front less than three minutes into the game - the 11th time in the past 13 games in which Ottawa has recorded at least one power-play goal - and he made it 2-0 at 8:52.
The Panthers rarely tested Emery through the first 20 minutes and fell behind 3-0 when Fisher scored a late shorthanded goal.
The second period didn't get any better for Florida and the deficit could have been larger without several excellent saves from Auld.
Kelly made it 4-0 at the 2:28 mark and Auld's night came to an end when Meszaros scored on a redirection at 6:01.
Ed Belfour entered the game to a chorus of boos from his days with the rival Toronto Maple Leafs. Vermette welcomed him by scoring on a rebound to make it 6-0.
Belfour finished with 10 saves the rest of the way.
The Panthers went 0-for-5 on the power play; the Senators were 1-for-4.
Notes: The game was delayed for almost 10 minutes in the first period when Florida's Stephen Weiss delivered a hard hit on Ottawa's Chris Phillips, shattering a pane of glass in the Senators' zone. A family of four, including two young children, was taken to hospital as a precautionary measure after being showered with broken glass. . . Ottawa defenceman Anton Volchenkov returned after sitting out the last two games with a lower-body injury. . . . Panthers centre Joe Nieuwendyk missed the game because of a sore back.