FDR, president for 12-plus years, was worn down by the stress of office, but perhaps more critically, he suffered from high blood pressure, which at the time medical science could do very little about. An article by in US News & World Report in 2005 by Daniel Levy and Susan Brink makes clear that the 32nd president lived a few decades too early to survive into old age (after all, he was only 63 when he died): "... severe blood pressure elevation such as he was experiencing can cause chest pain, as well as congestive heart failure, kidney failure, deteriorating mental function, and stroke," wrote Levy and Brink. "It represents a medical emergency. In that condition, the president undertook an arduous 14,000-mile round trip and spent a week orchestrating the final strategy for victory in Europe. He returned exhausted from his pivotal meeting with Joseph Stalin and Churchill in Yalta. As the war raged on, the commander in chief involved himself in discussions about a new weapon nearing readiness--the atomic bomb.
"He headed to his Georgia sanctuary at the end of March  for two weeks of rest. Those who saw him during his last days were shocked at how aged he looked. He was down 15 pounds from his normal range of 184 to 188. Suffering from orthopnea, a telltale sign of congestive heart failure, he had trouble breathing when lying down, and for months had been sleeping with 4-inch blocks of wood propping the head of the bed. The agent at the Warm Springs railroad station, C. A. Pless, accustomed to greeting a smiling, waving man who could never resist the crowd, said later, 'The president was the worst-looking man I ever saw who was still alive.'
"On the morning of April 12, Roosevelt donned a dark-gray suit, matching vest, and red tie to pose for a watercolor portrait by Elizabeth Shoumatoff. As the artist painted, he signed papers. Roosevelt lit a cigarette, raised his left hand to his temple, and then seemed to squeeze his forehead. As he reached for the back of his neck, he said, 'I have a terrific headache.' Then he lost consciousness. An excruciating headache is a classic symptom of a brain hemorrhage, a catastrophic form of stroke caused by a ruptured blood vessel in the brain. [FDR's doctor] Bruenn was summoned and within minutes took his patient's blood pressure. The numbers, an unsustainable 300/190, went well beyond an indication of danger. They were evidence that the tragedy had already occurred. Two hours later, at 3:45 p.m., the president was dead. Although no autopsy was performed, the cause of death was certainly a massive stroke.
"When Roosevelt died, doctors had little more than folk wisdom at their disposal to control blood pressure. To look at the picture of cardiovascular ignorance just six decades ago is startling. Heart disease, the most common form of cardiovascular disease, was so ubiquitous that it was considered an inevitable consequence of aging."