Two brothers are being called heroes for saving their grandmother's life months after learning CPR from their mother.
Kian and Grayson Wu, 10 and seven, were settling down to watch a movie at their grandmother's house in Saskatoon, Canada, on November 10 when she lost consciousness.
What the boys didn't know at the time is that Patti Chatterson, 62, had just suffered a major attack and had gone into cardiac arrest.
The family said they are now sharing their story as an example of the importance of learning CPR at any age.
Chatterson told DailyMail.com she lost memory from two days prior to the incident but has been able to piece together what happened.
'I had my grandsons over for the whole day, we went to brunch, had our dinner, and then we sat down to watch a movie together,' she said.
'My youngest grandson asked if he could have a snack. And when I didn't answer, he looked over and my head had fallen back, I was not breathing properly, and making funny noise. So they recognized something was wrong.'
Unlike many children their age, Kian and Grayson were prepared for such a situation.
Just five months earlier, their mother Lee Chatterson Wu, who is a nurse, taught them how to administer cardiopulmonary resuscitation (CPR) - but she never thought they would need it any time soon.
In June, Kian had a sleepover party for this 10th birthday and he and his friends asked Chatterson Wu to teach them.
'[I taught them] where to do compressions, how to do compressions, the breaths, plugging the nose, covering the mouth. It wasn't a very in-depth teaching of it,' she told CBC.
'I honestly didn't think they'd ever need it, or that it was necessarily an important thing to teach them at the ages of seven and 10.'
When the heart stops, the lack of oxygenated blood can cause brain damage in only a few minutes. A person may die within eight to 10 minutes.
CPR can keep oxygenated blood flowing to the brain and other vital organs until more definitive medical treatment can restore a normal heart rhythm.
CPR doubles the survival rate of patients who go into cardiac arrest even though only about eight percent of CPR patients are saved by the procedure, even when backup help is called immediately.
So when Chatterson collapsed, Grayson and Kian knew they had to act immediately.
The brothers first tried calling their mother and father on the phone, but neither of them answered.
So Grayson called 911 as Kian began chest compressions.
'We gave them our address, and then we told them that our grandma was unconscious and not waking up and not breathing and had no pulse,' Kian told CBC.
'And then we checked her nose, and she wasn't breathing.'
The emergency dispatcher, Allison Maffin, told the boys to lay their grandmother on the floor without any pillows.
Then, Kian continued compressing - so hard he accidentally cracked Chatterson's ribs - while Grayson plugged her nose and performed rescue breaths.
Paramedics arrived less than 10 minutes later and had to defibrillate Chatterson four times.
When she woke up in the hospital four days later, she was on life support and was told about her grandson's efforts to save her.
'I can't imagine what must have been going through their minds,' Chatterson, a former emergency room nurse herself, said.
'I was totally amazed. When I find out they witnessed it and acted it on it, I was so grateful they knew what to do.'
Despite doctors not being able to pinpoint why Chatterson went into cardiac arrest, she was released from the hospital and says she is recovering well.
Doctors outfitted her with an internal defibrillator, which is implanted inside the body and corrects on its own most life-threatening cardiac arrythmias.