The decision was taken by the club after a management meeting at the club’s secretariat.
Addo’s reign came to an end due to the poor run of form the team has experienced in recent months.
The Phobians were beaten by Medeama 2-1 in the MTN FA Cup semi final played in Cape Coast on Sunday and before that, they lost 2-1 to Hasaacas in the First Capital Plus Premier League.
Addo was appointed before the start of the current league season was tasked with sending the team to the top half of the league.
However, his record of 6 wins, 8 draws and 7 losses has pushed his employers to terminate his career.
Citi Sports has picked up information that former Black Stars goalie Edward Ansah will handle the team until a substantive coach is named.
There is speculation that former Amidaus and Berekum Chelsea coach Tony Lokko is the top favourite for the job at Hearts of Oak.
Before taking over at Hearts (for his second tenure), Addo coached Inter Allies in the 2013/2014 season and helped them finish 6th on the league log. He also led them to the finals of the MTN FA Cup where they lost to Kotoko.