My friend also had fast heartbeat after AZ jab until admitted into hospital, hover around 120 - 140 until 2nd day, 5 diff doctors went to check his condition, took blood test, did this and that but all result normal, at the end they concluded it as panic attack.

After 3 weeks he still felt weak especially when climbing stair, 1 floor already tired, cannot jogging, random pain on chest area. Went hospital to check again but still cannot find anything wrong.