With the magnitude and the pattern of morbidity and mortality from the multiple extreme heatwaves that occurred in 2023 still being determined, it is illustrative to review the human health consequences of a heatwave that occurred over a period of several days in late June and July 2021 in the north-west of the United States of America and Canada. This case study is part of the publication “Adaptation Gap Report 2023: Underfinanced. Underprepared. Inadequate investment and planning on climate adaptation leaves world exposed” (ISBN No: 978-92-807-4092-9). Suggested citation: The Pacific heat dome: Heatwave lessons from the United States of America. An online resource of Adaptation Gap Report 2023: Underfinanced. Underprepared. Inadequate investment and planning on climate adaptation leaves world exposed. Nairobi. https://doi.org/10.59117/20.500.11822/43796