The island is Springbank Island in Lake Burley Griffin and after some investigation we were able to track down who the lawn mower was.
However, their identity will remain a mystery.
A spokesperson for the National Capital Authority said "the lawn mower etched their message in a grassy patch of Springbank Island in West Lake, took a photo and sent it to their sweetheart, believing the heartfelt gesture would be a private affair. As such, we will need to leave the online world wondering who they might be".
Adrian suspects the heart can only be seen from the air, so it was a happy coincidence he managed to capture it.