In March 1935, Eden had an exhausting trip with Viscount Cranborne (the future Lord Salisbury) to Paris, Berlin, Moscow, Warsaw and Prague. On his flight home, his plane was caught in a severe snowstorm, and had to land in Cologne. Eden had been so shaken and airsick, with a pulse rate of only 40 per minute, that he was immediately seen by a doctor who pronounced his heart "sehr schlecht" — very bad — and put him to bed in a hotel. The next morning, a specialist was equally gloomy about Eden's heart and vetoed his plans to fly home. He returned to London by train and boat. King George V telephoned and ordered him seen by Sir Maurice Cassidy, the royal heart specialist. The electrocardiogram was said to show heart strain, and he was sent to a nursing home for four weeks, followed by two weeks at home. Naturally, there was a bulletin: "Mr Anthony Eden is suffering from heart strain resulting from his recent rough air journey. There is no cause for anxiety, but complete rest is essential for from four to six weeks." This was followed by a dozen almost daily bulletins in The Times until the last on 9 May: "He has now recovered from the overstrain and will resume his work at the Foreign Office next month."

In retrospect, I consider that on his flight, Eden had an episode of vasovagal syncope (fainting), and not a myocardial infarct (heart attack), and his six weeks' rest was unnecessary. Nevertheless, as a
result Eden missed the Anglo-Franco-Italian conference at Stresa on 11-14 April. Before they travelled to Stresa, the Prime Minister (the demented Ramsay MacDonald) and his Foreign Secretary (John Simon) visited Eden, who has stated that he implored them to ensure that the conference faced up to German rearmament, agreed to prevent the Nazis from annexing Austria and stopped Italy invading Abyssinia. The British ministers, even when prodded by Robert Vansittart (the Foreign Office permanent under-secretary), failed totally. A French paper detailing the German army's activities in the Rhineland was not presented, nor was the integrity of Austria and Abyssinia guaranteed. MacDonald by now was mentally almost incoherent and Simon unassertive. Eden later implied that if he had been there "Stresa might have influenced history" as a last chance to prevent the Second World War. His speculation is most unlikely because by then the appeasement of Germany was irreversible and war inevitable.

Eden was troubled from the 1920s by ulcer pain. He was periodically tired, exhausted and unwell during the war, with a recurrence of his duodenal ulcer in 1945. In March 1953, Marshal Tito commented on Eden's colour. Eden was indeed jaundiced and X-rays in April showed gallstones. Sir Horace Evans advised an immediate operation by one of three biliary surgeons he recommended, but Eden insisted on choosing the general surgeon who had removed his appendix in 1948. On 9 April, the gall bladder was removed but other structures were damaged. A second three-hour operation saved his life, and he was advised to have a third operation by Richard Cattell in Boston. This eight-hour operation in May stabilised his condition, but Cattell warned that there would probably be further episodes of cholangitis (inflammation of the biliary ducts). Cattell was proved right in his prognosis. 

Eden returned to London to find Churchill back at work. For the next two years, Churchill frequently promised to resign only to recant. Eden was left ever more frustrated and embittered. However, like Lord Rosebery, Foreign Secretary in Gladstone's last premiership, Eden was too loyal to plot against his leader. Horace Evans had agreed that Eden's health could allow him to succeed Churchill. Eden was left with the Suez problem that ended his career.

 
Eden: Forced to resign through ill-health