The bullet went into the chest, collapsing the lung, and caused bleeding out into the chest cavity.
Chest tube is indicated.
However, the guy flatlined, and in that case the meds of choice, correctly given by Gant, are epinephrine and atropine, both of which could possibly restart to heart. CPR was administered by Carter, but they all decided the ever present thoracotomy and open chest massage was to be used. While in the chest they clamped the area that was bleeding, and the guy suddenly decided to partially recover, thrashing everything around, and probably getting infected. Then he went flaccid again. I thought he dies originally, but reviewing the video the monitor did still record a heartbeat.