Below is an image believed to be similar (if not the same) of the bullet as it came to rest in Trayvon Martin. The bullet entered in the area so marked and came to rest near the heart, piercing the left ventricle, and of course not exiting the body as hollow-point bullets are designed to do.
We do not yet know whether Trayvon suffered cardiac tamponade, an effect caused by rapid loss of blood within the pericardium, thus compressing the heart or whether it was simply exsanguination or bleed-out that caused death. We do know that Trayvon was in an excited state and may very well have been doped with a far higher than normal cardiac output, leading to possible cardiogenic shock before exsanguination or tamponade.
My assumption is Trayvon was over George with his body lower down the centerline of George due to placing himself for the most effective blows to George’s upper body and head. It is very likely Trayvons left hand (left-handed) was gripping the KelTec thus pulling the weapon closer to the left side of the chest. The single bullet fired (the semi-auto did not fully cycle) traveled in a downward path striking the heart.
Had this shot not been effective, George would not have been able in all likelihood to have cleared the spent casing and fired again. On the other hand, I suspect Trayvon was not adept at using a firearm and he himself would have been unlikely to have made the gun discharge another round.
The KelTec performed as expected as did its’ first round, in spite of the fact that cycling of the semi-auto was somehow blocked. Had George truly been the aggressor, he would have fired long before Trayvon was on top of him.