>> our phoenix station knxv introduces us now to our hero. >> my grandma came to their to look for her toothpaste and she said, where's the baby? and my mom went running outside. and there she was floating and then i heard her screaming and i was like "oh my gosh, what is happening?" >> reporter: pulled out of family pool, tristan's 2-year-old sister was placed on the ground unconscious and not breathing. she was dying. tristan's mother and grandmother were frantically calling for help and frightened, but tristan, he was cool and calm. >> i went running outside. and i did cpr on her. >> reporter: this 9-year-old boy took control. he began to begin chest compressions on his little sister. his hands in the right place. >> and i then like give them oxygen, like -- >> reporter: long, stressful minutes went by and then -- >> she started breathing a little bit. >> reporter: paramedics took tristan's sister to the