Heffernan completed his second win of the season, and third of his career, at 18-under-par 266.
Anthony Rodriguez (65) and Adam Speirs (68) shared second place at 13-under- par 271. Adam Bland, also a two-time winner this year, posted a 68 to share fourth with Stephen Gangluff (67) at minus-12.
Heffernan led by five entering the final round, but a bogey at the first gave the rest of the field a glimmer of hope. However, he birdied the third to erase that mistake, then posted his fourth birdie in four days at the par-5 fourth.
The 30-year-old birdied the sixth and eighth at Club de Golf El Tigre to make the turn at 18 under.
Heffernan, who won the Northern California Classic earlier this year, birdied three of the first six holes around the turn to soar to 21 under. His large lead was trimmed by a triple-bogey at the par-4 16th. No matter, he parred the final two holes for a five-shot win.
'It was a weird feeling having that lead,' Heffernan stated. 'It's not as comfortable as you would think. I was nervous after that bogey on one, but got into a rhythm after that.'
Rodriguez also bogeyed the first, but bounced back with five birdies on the front nine. Around the turn, he posted two birdies and seven pars to share second at 13-under.
Speirs had an up-and-down round with six birdies and three bogeys to join Rodriguez in second.
Travis Johnson, Alan McLean and Brendan Steele shared sixth place at nine- under-par 275, while Graham Delaet and Antonio Maldonado were one stroke further back at minus-8.