TORONTO -- MLS prospect Zachary Herold has ended his soccer career at 17 because of a heart condition.
Herold is a defender for Toronto FC who also has made 15 appearances for the U.S. under-17 team.
His condition causes abnormal thickening of a part of the heart muscle. Strenuous exercise carries the risk of a potentially fatal irregular heart rhythm. The problem was flagged in a preseason medical