Van Heerden is a free agent following his departure from Pirates last week, having struggled for game-time in an 18-month spell with the Soweto giants.
The 30-year-old left-back spent eight years with Usuthu before brief stints at Chippa and Bucs.
Right-back Sikhakhane, who was on loan at AmaZulu last season, has also failed to establish himself at Mayfair since his arrival from Golden Arrows two years ago.
According to a source, the duo are seemingly heading back to Durban.
"AmaZulu have shown huge interest in Van Heerden," says the informant.
"The deal could go through before the end of this week.
"The club is also close to finalising a permanent deal for Sikhakhane."