HANOVER, N.H. — An autopsy has determined that a rare heart defect killed a 20-year-old Dartmouth College cross country skier last weekend.

Torin Tucker, a junior from Sun Valley, Idaho, died while competing at a cross country skiing marathon in Craftsbury, Vt., on Saturday.

His death certificate says he suffered sudden cardiac arrest as a result of a problem in the left coronary artery. Medical research says the condition is rare and is frequently associated with sudden death during intense physical activity.