The first president to die in office was William Henry Harrison, he died after contracting pneumonia. When John Tyler died he became president. The second president to die in office was Zachary Taylor, who died of acute gastroenteritis. His successor was Millard Fillmore. President Warren G. Harding also died in office of natural causes, suffered a heart attack, and Calvin Coolidge became president. The last president to die in office of natural causes was Franklin D Roosevelt, who died of a brain haemorrhage. Upon his death he became Harry Truman