My dad survived 19 punctures from a Fallow buck about 10 years ago. The surgeon that sewed him up said the puncture in his chest was such that he could reach in and touch the sac around his heart. He was very lucky, and lucky that it was a Fallow vs something with straighter horns like a Whitetail or Axis.
Same deal, he went into a pen to turn off a sprinkler. In hindsight he recalled this and another male pushing each other around but didn't think much of it. The attacker came over and lowered his antlers for a head scratch like usual and as soon as dad touched his forehead, the buck attacked. Lesson learned, beware of caged, tamed animals.