"He was basically a big bundle of fun," fellow student Sarah Braden told 7NEWS Reporter Christine Chang Sunday. "Because he was super tall (and) always made fun of me for being short."

Braden said Hammerdorfer, an avid multisport athlete, taught her to live life to the fullest and not take it so seriously.

"He was very caring," she said. "He always had your back whether he knew you for a day or a year and a half."

Teen Athlete Dies Of Sudden Cardiac Arrest

Hammerdorfer, a 17-year-old junior at Poudre High School, collapsed during a rugby game in Timnath Saturday afternoon.

Witnesses said he took a hit on the field, fell down and didn't get up.

"We got reports that the victim was in seizure at some point before and during our response," said Patrick Love, spokesman for the Poudre Fire Authority.

Hammerdorfer was flown to Medical Center of the Rockies, where he later died.

Larimer County Deputy Coroner Kari Jones said Hammerdorfer died from complications of a congenital heart condition.

A Sunday morning autopsy listed the cause of death as sudden cardiac arrest due to cardiomegaly and biventricular hypertrophy. The coroner’s office explained to ABC News that cardiomegaly refers to an enlarged heart and biventricular hypertrophy refers to enlarged ventricles.

Hammerdorfer suffered from both as a result of being born with a heart defect called tetralogy of fallot, for which he had surgery at age eight, the coroner's office said.

Matthew Was Very Popular At Poudre High School

"Poudre High School students and staff are saddened by the loss of Mathew Hammerdorfer," Principal George Osborne said in a Sunday statement. "Matthew was a very popular student. He was always upbeat and positive and had a zest for life. Matthew was very involved in school, both academically ... and as a multisport athlete. When talking with teachers over the weekend, they spoke very highly of Matthew. Our thoughts and prayers are with the family."

Counseling teams will be there for students at the school Monday, Osborne said.

Athletes At Higher Risk For Underlying Heart Conditions

Hammerdorfer's death spurred debate about whether young athletes -- and even older ones -- should under regular heart-monitoring tests.

It is estimated that one in every 350 children may have dangerous underlying heart conditions, ABC News reported.

"Athletes are at higher risk than the general population because they exercise more," Dr. Jonathan Drezner of the University of Washington told ABC News Sunday.

"And ironically, although we know that exercise is a healthy benefit for all of us, in some persons with an underlying heart condition exercise can actually be the trigger for a sudden cardiac arrest event," he said.

Hammerdorfer's death came just days after Michigan high school basketball player Wes Leonard collapsed and died after scoring the winning shot for his team, leaving his coach, team and the community devastated.

Heart Screenings Vs AEDs

ABC News said teenagers and young people dying of heart failure is far more common than might be expected: An average of 40 young athletes die from heart disease in the United States is per year, or approximately one death every nine days.

Parent Heart Watch is one support group that is trying to encourage awareness and preventative measures that will avert such tragedies. They say young athletes should get early and mandatory screening with an electrocardiograph (EKG), which tracks heart activity over time, ABC reported.

Other groups also want schools and teams to have heart defibrillators at games, and have coaches and parents learn CPR.

The European Society of Cardiology and International Olympic Committee endorsed standardized screenings that have been credited with lowering cardiovascular deaths in Italy. That country passed a law in 1982 requiring athletes of all ages to undergo electronic heart testing every couple years.

But medical groups in the United States have recommended against implementation of such a system, saying the high costs outweigh the benefits.

Some experts say the money would be better spent putting automatic external defibrillators at every sporting event than on EKG screenings.

Dr. Douglas Zipes, editor of Heart Rhythm, told ABC News that to cover the $1,200 cost of a defibrillator, "you could get 120 fathers to kick in 12 bucks each."

Mom: Can't Put Price-Tag On 'Peace Of Mind'

But a flurry of comments posted on TheDenverChannel.com's Facebook page strongly supported the value of precautionary heart testing.

"My son is a HS athlete and we have always used our family doctor for his yearly physicals...and every year an EKG is included," a mother wrote. "In his sophomore year his EKG had an abnormality -- We then had to follow up with an ECHO of the heart and an appointment with a cardiologist.

"DEFINITELY worth every penny and the amount of time it took. All was well and he was cleared for participation! You can not put a price tag on 'peace of mind,'" the mother stressed.

Another woman said: "Yes I would!" pay for heart testing. "My ex-husband was suddenly diagnosed with Severe Hypertropic Cardiomyopathy. We never saw it coming. I think all athletes should have this test."

Friends Remember Matt

Friends and family of Matthew Hammerdorfer shared memories of the teen Sunday on a Facebook memorial page.

"Matt you're more than my brother. You have made life worth living even when you are gone," Tim Thompson wrote on the website. "I love you man forever and always. Riding the clouds in your old hippie van with dreads flyin out the window. So now i say goodbye without an ounce of regret for my fallen brother who will be walking side by side with me on my road to Zion. Peace and Love Matt."

Braden remembered her friend's love for rugby.

"He wanted to play all the time," she told 7NEWS. "That is where he wanted to be ... on the field playing with his friends."

Ultimately, the girl said, Matt "made me realize that life is fragile."