November 1953 (age 54)

Sig edits and returns Devereux Butcher's lead piece for the forthcoming National Parks Association book Exploring our National Parks and Monuments . He deleted sections in which he thought Butcher was questioning the motives of other conservation groups ["It weakens the cause to do so and detracts from the dignity and beauty of the writing"] and paragraphs that attacked the National Park Service. He said:

While again it is true, it will serve no purpose but to antagonize the Park Service. I saw enough of unwise developments within the parks this summer and I can assure you I feel as you do, but I do not think your leading chapter should call names or make the National Park Service appear as lacking in understanding. There are other ways of accomplishing our end....What is needed is an educational campaign in which the National Parks Association can participate as it has done in the past....We have to work with the NPS and in this case by getting its full support, we will be far ahead when it comes to distribution in the National Parks.

November 1968 (age 69)

On November 22, Sigurd and Elizabeth were at Casa Ybel Resort on Sanibel Island off the Florida Gulf Coast for the annual meeting of The Wilderness Society. Sigurd had just become the organization's president. During the opening dinner, he suddenly grew pale and clutched his chest. Frantic, Elizabeth called out for help. Wilderness Society executive director Stewart Brandborg helped Sigurd out of his chair and onto the floor, while others scrambled to get medical help. Hotel staff located a vacationing doctor from New York City, who came and cared for Sigurd until a resuce squad arrived.

Sigurd had suffered a major heart attack. He spent three weeks in Lee Memorial Hospital at nearby Fort Myers, the first three days in intensive care. Letters and cards and flowers arrived from friends across the United States and Canada. After ten days in the hospital he was able to get out of bed long enough to walk to the bathroom, which he took as a sign that he was mending. But even after he left the hospital in mid-December, he was far too weak to travel home. Instead, he and Elizabeth leased an apartment at the Seacrest Motel in Sarasota, ninety miles to the north along the coast.

They stayed in Sarasota until February 1969. Sigurd gradually worked his way up to several slow walks a day along the beach and enjoyed an occasional restaurant dinner of shrimp rolled in flour and broiled in beer. His doctor told him he absolutely could not give any talks or go to any meetings for at least six months and warned him to change his lifestyle for good if he wanted to avoid a killing heart attack.