The home pack were in control early on and that led to two penalties being kicked by Simmers in the 11th and 15th minutes.
With one of their first attacks, Gala scored a converted try when a kick into the dead-ball area by Gregor Hunter caused confusion and Rob Louw touched down. Hunter converted.
Heriot’s then scored two tries in six minutes, the first at the end of the first quarter when No 8 Struan Dewar went over, followed by a score from Charlie Simpson.
That made it 18-7 and a Simmers penalty extended that to 21-7 before a second Gala try.
The converted effort came from Rory Scholes, making it 21-14 at the interval.
Heriot’s came out flying after the break and they scored a well-worked team try in the 43rd minute.
Simmers went over for the converted score, putting Heriot’s 28-14 up and chasing a bonus point.
And they clinched that in the 55th minute, Simpson getting his second of the afternoon.
Simmers also got his second before a late Ross Combe try for Gala.