 Graves died of a heart attack on July 19, 1965 while skiing in Del Norte, Colorado, twenty years after the Slotin accident, at the age of 55. He had suffered from hypertension even before the 1946 accident, and had a minor heart attack in December 1955. His father had also died of a heart attack. A 1978 follow-up study of the Slotin accident victims suggested that latent systemic damage from the accident contributed to heart failure. He was interred in the Guaje Pines Cemetery in Los Alamos, New Mexico.
