Four Presidents have died by natural causes, Harrison, Taylor, Harding and Roosevelt. Four Presidents have been assassinated, Lincoln, Garfield, Mckinley and Kennedy.
William Henry Harrison  died of pneumonia on April 4, 1841, the shortest presidency in the United States.
Zachary Taylor [1848-1850] died of gastroenteritis on July 9, 1850.
Warren G. Harding [1921-1923] died of a heart attack on August 8, 1923.
Franklin Delano Roosevelt [1933-1945] died of a cerebral hemorrhage on April 12, 1945
Abraham Lincoln [1861-1865] shot by John Wilkes Booth on April 14, 1865.
James A. Garfield  was shot by Charles J Guteau on July 2, 1881 and died from those wounds on September 19, 1881.
William McKinley [1897-1901] shot by Leon Czolgosz on September 6, and died on September 14, 1901.
John Fitzgerald Kennedy [1961-1963] shot in Dallas, Texas on November 23, 1963 by Lee Harvey Oswald.