Stunned heart muscle does not recover as rapidly as hibernating heart
muscle. But in contrast with infarcted
heart muscle, in which many
muscle cells are dead, it does indeed recover. Function in the stunned heart muscle may not return for 10 to 16 days after the restoration of blood flow.
To answer your question of how long depends on whether the heart cells are stunned, hibernating or necrotic...or combination of the 3 variables.