Heaney, 21, joined the Seasiders from West Auckland Town this summer and was previously a highly-rated prospect at Newcastle United.
Grindavik play in the second-tier in Iceland, having been relegated at the end of last season and their season kicked off on June 19.
Manager Chris Hardy said: "With the delayed start to our season, this is an opportunity for Mackenzie to get some game time.
"This is priceless and much better than him being sat at home just working on individual fitness work.
"We want him match-fit and this move will put him in good stead to come to us in pre-season and to then hit the ground running."
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