The 57-year-old, born in Rowley Regis, suffered the incident in the first mile of the run, but managed to complete the course before leaving for hospital, where he had tests.
Palmer, who came through at Albion before leaving for Sheffield Wednesday in 1989, stayed in hospital overnight before updating fans on his Twitter account at 3am.
He tweeted: “Just to let everyone know I am ok, being kept in overnight in hospital observation/tests. Heart played up again in the first mile but I managed to complete the course. Congratulations to my gorgeous wife for going sub two hours love you.”
In another tweet, he added: “Thank you so much for all the lovely messages I have being kept in hospital with a suspected small heart attack, they want to find out what has caused this problem so tests are ongoing. I will keep you updated. Gutted I was flying to Portugal at 4pm with Lucy.”
This comes after Palmer had a life-saving operation in December 2016 after a heart condition was discovered.