and now the case of matthew hammerdorfer. >> reporter: 17-year-old rugby player matthew hammerdorfer powerful hit to the chest and died. it's caused by a condition known as sudden cardiac death. experts say it happens far too often to young athletes in the prime of their life. it's estimated as many as 1 in 350 kids may have dangerous underlying heart condition. >> athletes are probably at higher risk than the general population because they exercise more. ironically, we know exercise is a healthy benefit for all of us. in some persons with an underlying heart condition, exercise can be the trigger. >> reporter: matthews death comes just day, after michigan high school basketball player wes leonard collapsed and died after the winning shot for his team. >> it's just tearing me up. he was just a kd with a passion you that just don't get to see all the time. >> reporter: young people dying of heart failure, it's far more common than most of us realize. stories like these are being repeated around the country. with estimates as high as one death every three days. support groups like par

friends say matthew hammerdorfer was always smiling, always ready with a joke. and now many are calling for new attention to a most serious problem. clayton sandell, abc news, ft. collins, colorado. >> story so difficult to hear. we want to bring in dr. marie savard, an abc news contributor. and i know you have three sons, all young athletes. you are so versed on this. i wanted to look at this animation of the heart tonight. and it starts out as a heart that's normally beating. >> that's right. sudden cardiac death goes from a normally beating heart to a very rapid beating heart and then an erratically beating heart and it stops, often because there's an underlining, a congenital condition, as we're learning in this case tonight, perhaps a heart disorder that wasn't yet discovered. >> so the parents had no idea. >> that's right. >> which leads to your checklist tonight. they're going to hear what they do in italy, the ekgs, many parents will want to ask for one. what's the recommendation on that? >> the american heart association recommends two things. first, th

family and friends are mourning 17-year-old matthew hammerdorfer who was playing in a youth rugby football match saturday in fort collins, colorado. hammerdorfer had been knocked down. a teammate recalled what happened next. >> he got up, and he started to walk a couple of steps and then he just collapsed. >> hammerdorfer died later at a hospital. doctors say he had a congenital heart defect and the hit he took on the field was not a contributing factor to his death. >>> in southwest michigan hundreds of people attended a visitation for another teen athlete who died last week, 16-year-old wes leonard of fennville, michigan collapsed on his high school basketball thursday night just after scoring the game's winning shot. an autopsy showed he died from an enlarged heart. >>> in health news, massachusetts general hospital in boston will conduct this country's first 3-d mammogram on a regular patient today. the process, which has undergone clinical trials, gives doctors a significant new tool for detecting breast cancer. it locates a tumor or a lump precisely and costs no more than standard ma

two communities are in mourning today over the sudden deaths of star athletes. 17-year-old matthew hammerdorferool rugby team. during a match on saturday, took a hit to the chest, then collapsed. an autopsy found that he died due to congenital heart defect. just two days earlier, 16-year-old wes leonard collapsed and died on a michigan basketball court after his game-winning shot. now the cause of death was determined to be an enlarged heart. medical correspondent dr. jennifer ashton is here with more on these conditions. >> good morning, chris. >> let's talk about harver dorffer first. the autopsy says sudden cardiac death. let's talk a little bit about this, exactly how this caused this to happen? >> that's really a catch-all term that is commonly the listed cause of death. in his case it was due to a congenital heart defect. there are about 35 babies born in this country every year with what's known as conseine tal heart defect. in his case, it had four different types of problems in the heart. it's usually surgically corrected at three to six months. in his case he had at least one operatio

. >> reporter: 17-year-old matthew hammerdorfer was doing what he loved this weekend, playing rugby oneld in ft. collins, colorado, where he collapsed and later died. it was a sudden cardiac arrest. this morning, facebook is awash with emotional tributes. you are more than my brother. i love you, man. you will never be forgotten. it comes just days after a 16-year-old basketball star in michigan named wes leonard collapsed on the court and died from sudden cardiac arrest moments after making the winning shot. the crowd going from jubilation to horror. >> this is just tearing me up. because he was just a special kid with a passion. you just don't get to see all the time. >> reporter: these two cases are hauntingly and infuriatingly familiar for michelle snyder whose 17-year-old daughter jennifer died after cardiac arrest during soccer practice. >> she kissed me good-bye and said i love you. i said i love you too. >> reporter: now snyder is running an organization that calls for placing defibrillators in gyms and parks and making sure teachers and coaches are trained in cpr. >> all of a

comes less than a week after two other high school athletes died. 17-year-old rugby player matthew hammerdorfer and 16-year-old basketball star, wes leonard. leonard's team won their second game without him last night. but he was in their hearts and on their backs. both male athletes had heart problems. this morning, it's still not clear what caused sarah's death. >> we had school go on as usual. but we've been flexible to give kids a chance to talk about their emotions. >> reporter: and grief counselors will be at the school again today to help students deal with their emotional loss. elizabeth? >> all right, ryan. thanks so much. >>> we're joined now by dr. merrill meyerson, a cardiologist that specializes in sports medicine. this star athlete had to have cpr two weeks ago. how was she cleared so quickly? >> it's hard to go back and second-guess. but we hope she had a thorough examination by a qualified provider. hopefully an electrocardiogram and maybe even an ultrasound of her heart. >> based on your experience in exercise physiology, what do you think happened? >> most cases such as this,