He should get checked out by a doctor before any more strenuous exercise. The media is full of stories of athletes dropping dead of cardiac arrest. It could be nothing, but if there is a problem with his heart, he could get treatment.
I agree with BionicBabe - definitely get him looked at for safety sake before letting him practice or play. It could be nothing or something but when you see young athletes with debilitating heart rhythms you worry about WPW, ARVD, hypertrophic cardiomyopathy, coronary artery abnormalities or, to a lesser degree, idiopathic arrhythmias. Except for coronary artery abnormalities you can go a long way towards ruling out these problems with an EKG and echocardiogram. The good news is that most of the big problems are quite rare. Where is your host son from?
Venticular Tachycardia or VT is the number one killer among young people especially athletes in the US today. This is what the media calls sudden death or sudden cardiac arrest. Take your boy to a Cardiologist as soon as possible. PLEASE!!!!!!!
Did you ever get a diagnosis for your host son?