It was near midnight on the side of the road - his mother doing CPR on his little brother in the back of the car - when Koby Johnston dialled triple zero.
The 12-year-old helped to get paramedics on scene within four minutes, and has earned not only their admiration but their recommendation for a bravery award.
The Tamworth youngster is credited with having helped to save the life of Jax, 3.
"He's a little hero," paramedic Todd Wheeler told the Leader.
Jax has myocarditis - an infection around the heart - and in September was struck down by a virus, mother Jesse bundling the boys into the car to rush to Tamworth hospital.
En route, Koby noticed Jax wasn't breathing. His mum pulled over and started first aid.
"He stayed on the phone to triple zero and told them everything he could, what we needed to know until we got there," Mr Wheeler said.
Mr Wheeler and his partner found the car on Ebsworth Street; he realised it was a family he'd seen about 18 months earlier, saving Jax's life after his first cardiac arrest.
"For someone in cardiac arrest, the survival chances are pretty slim, and it does increase with early intervention, resuscitation and defibrillation," he said.
"Koby started that process, and he even did better to jump on the phone to triple zero, in what was an intense situation already, especially given it was his little brother.
"It's jobs like these, it's what we kind of join the job for: to help people in their darkest hour."
Koby's help "really was a hero act".
"Luckily, we got to him at the right time - and that was a pretty amazing effort, for such a young boy to do what he did for his brother.
"It's so important that people know basic CPR. Recognising the signs or the symptoms early makes the difference ... For someone so young, recognising early that his brother wasn't breathing was a vital sign."
Paramedics are now putting Koby up for a bravery award, or a star award.