The Danish winger signed an 18-month contract with the Tynecastle club in January 2018, after leaving FC Copenhagen.
He arrived with three goals in 95 games for the Danish capital club under his belt as well as 61 appearances for his country from Under-16 to Under-21 level,.
Amankwaa had spent time on trial with Chelsea and in his early career, had been linked with Ajax and Arsenal.
However, he made just 16 appearances in all competitions for Craig Levein’s side, with questions over his fitness levels.
The wide man was taken out of the Hearts first team in February last year and put through rigorous sprint and endurance training in a bid to improve his stamina.
The 24-year-old was again told to work on his fitness in July, after the club found him to be “behind in his physical conditioning” on his return from a summer break.
Levein said at the time: “Until he gets to the level I need him at, he will be doing extra work and he won’t be playing in the first team.
“He actually has good technical ability and good speed, but he needs to be able to maintain that speed for the length of a match. At this moment in time he can’t do that, so we’re still working on him. He has a bit to go.”
A statement from Hearts read: “Danny returns to Denmark in search of more regular first team football and the club would like to wish him well in the future.”
Amankwaa will link up with former Hearts fans’ favourite Eggert Jonsson, who joined SønderjyskE in 2017.