Quoting Wikipedia's description of the scene:
Heck threatens to shoot Ryszard, ignoring Antonina's pleas as he drags her son away. A shot rings out and Antonina collapses. Ryszard returns unharmed, and Heck leaves the zoo for good. Antonina and Ryszard join the march out of Warsaw, bringing a rabbit and one of Heck's young bison. As they leave their home and the city is liberated, they release the bison into the woods.
The implication as you watch it is certainly that Heck has shot Ryszard; Antonina is pleading Heck not to shoot him and then we hear a shot, and Antonina collapses in grief.
A minute later, however, we see that Ryszard wasn't in fact shot; he walks over to his mother, unharmed.
I can't figure out what Heck did shoot there, or, if he didn't shoot anything, what the point was of throwing away the shot. Why would he shoot nothing, or, if he didn't shoot nothing, what did he shoot?