It was announced earlier this week that the 20-year-old playmaker switched allegiance to play for the country of his birth despite playing in all age-group teams for England including the Junior World Championship with England U20 last June in South Africa.
Heathcote is one of four changes on the Scotland bench while there is five changes in the starting line-up.
In the back line, Henry Pyrgos, who scored Scotland’s try against South Africa last weekend, is handed the starting jersey at scrum-half for the first time instead of Mike Blair while Max Evans comes in at outside centre for Nick De Luca who is on the bench.
Up front, Ryan Grant has not recovered from a calf injury sustained against South Africa last week. His place in the starting XV will be taken by Bristol loosehead Kyle Traynor with Gordon Reid coming onto the bench.
Scott Lawson will begin his first international since August 2011 at hooker pushing Ross Ford out of the matchday squad as Dougie Hall covers the bench.
At lock, Alastair Kellock gets the nod over Jim Hamilton to win his 47th cap, while in the back-row Alasdair Strokosch is restored from the calf injury that prevented his involvement against the Springboks.
On the bench the uncapped Edinburgh lock Grant Gilchrist is set to make his debut alongside Heathcote.
At the other end of the experience scale, substitute Newcastle scrum-half Rory Lawson is back on Scotland duty for the first time since the 2011 Rugby World Cup match against Argentina.
Scotland head coach Andy Robinson said: “We will not be among the top eight seeds for the 2015 Rugby World Cup draw, so this weekend I’m looking at giving a number of players an opportunity to put their hand up for selection for next year.
“This weekend we have to put together an 80 minutes performance and build on the positive parts of our games that we showed in the last 30 minutes against South Africa and the second half against New Zealand.
“International rugby is about pressure and it’s important that you convert your pressure into points and when you are under pressure that you are able to absorb it as opposed to conceding points as cheaply as we have done.”
Tonga have made a just one change for Saturday’s Test with Scotland in Aberdeen with Northlands flanker Hale T-Pole replacing Leicester‘s
The rest of the team is unchanged from the 15 that started the 22-13 win over the United States at Colwyn Bay last weekend.
London Irish
Tigers star Mafi is among the replacements along with Llanelli second row Sione Timani as Tonga seek their second win of their European tour.
Scotland: Hogg; Lamont, Evans, Scott, Visser; Laidlaw, Pyrgos; Traynor, S. Lawson, Murray; Gray, Kellock; Strokosch, Brown (capt.), Denton.
Replacements: Hall, Reid, Cross, Gilchrist, Barclay, R. Lawson, Heathcote, De Luca.
Tonga: Lilo; Vainikolo, Hufanga, Piukala, Helu; Apikotoa, Moa; Taumalolo, Taione, Aulika; Tu’ineau, Lokotui; T-Pole, Latu (capt.), Ma’afu.
Replacements : Ma’asi, Mailau, Sakalia, Mafi, Timani, ‘longi, Paea, Fatafehi.