When Heskey consigned Sunderland to their 11th away defeat of the season with his successful header it was his first goal in 14 games.
Birmingham, however, still struggled to destroy a weak Sunderland side that is already destined to make a hasty return to the Championship.
The Black Cats' lack of firepower was embarrassing and only emphasised the lack of investment which is proving to be their downfall.
The pressure of this game was evident from the start with Birmingham on the attack and Sunderland defending deep in an attempt to salvage a point.
It was important that Birmingham gained control but it was a difficult task in the circumstances.
With both clubs in such a dire situation it was hardly surprising there was little incident of note in the opening half hour.
Birmingham suffered a setback when they lost Damien Johnson with a knee injury after 25 minutes, giving Nicky Butt the opportunity to make amends for his recent transgression.
Bottom of the table Sunderland may have been showing an improvement in recent games but they are so far off the pace that they are already doomed.
Their makeshift side could make little impact on Birmingham's injury-hit defence, which lacked the services of Kenny Cunningham and Matthew Upson.
Sunderland's defiance fizzled out in the 39th minute following an incident in which Nyron Nosworthy was booked for a tackle on Jiri Jarosik.
Jermaine Pennant, who had previously tested Sunderland's defence with some skilful play, took the free-kick out on the left and his cross eluded everyone expect Heskey.
The former England striker managed to glance the ball into the top corner to ease the growing pressure at St. Andrew's.
In the second half Birmingham introduced DJ Campbell for the injured Chris Sutton to give him another opportunity to shine against Sunderland, after his two-goal performance for Brentford a few weeks ago knocked the North East club out of the FA Cup.
But it was Heskey who continued to be the main danger as he demonstrated with a close-range header from another tantalising cross from Pennant.
The livewire Campbell went close to opening his Birmingham account but his shot was blocked and visiting keeper Kelvin Davis prevented Heskey profiting from the rebound.
Sunderland gamely attempted to get back into the game and the former Southampton player Rory Delap attempted to mark his first appearance with an equaliser after he had gained possession following a weak tackle by Julian Gray.
Unfortunately, his effort was just off target as Birmingham anxiously survived a difficult spell.
The introduction of David Dunn for Muzzy Izzet made a difference and only a brilliant finger-tip save by Davis prevented a second goal.