Helmick died early this morning at Iowa Methodist Medical Center. He was 66.
A hospital spokeswoman says the Des Moines attorney died of cardiac failure. His law partner says Helmick suffered a stroke over the weekend.
Helmick served as USOC president from 1985 to 1991.
He became the first International Olympic Committee member to resign under pressure in 1991 after being accused of using the position for personal gain.
A USOC investigation into allegations of influence peddling by Helmick found no wrongdoing. Helmick resigned anyway, saying the controversy was disruptive to the committee.
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