Joe Ledley, Amido Balde, Charlie Mulgrew and a Lee Ashcroft own goal secured a 26th game unbeaten for Neil Lennon's side in the league.
It took the hosts at Parkhead just 11 minutes to open the scoring as Ledley raced onto a pass from James Forrest to fire low into the bottom corner.
Ashcroft doubled their lead 10 minutes later as he turned a Forrest cross into his own goal, Mulgrew added a third before Balde secured the win with a last minute strike.
Hearts meanwhile collected a second successive victory to move onto five points at the bottom of the table, having only moved into positive figures last weekend.
Steven Thompson gave St Mirren a great start at Tynecastle with a goal in the opening minute of the game, but Hearts were only behind for four minutes as Callum Paterson levelled with a close-range header.
Victory was assured for the hosts in the 51st minute as Jamie Hamill scored from the spot following Marc McAusland's challenge on Dale Carrick, a challenge the defender received a straight red card for.
Hearts remain rooted to the foot of the table despite the win, with the gap to Partick Thistle now 16 points.
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