Several British soldiers fainted in the heat during a performance on Saturday.
Video footage showed one guardsman lying on the ground with his trombone in hand as medical help rushed to tend to him.
In the background, another guardsman was carried off on a stretcher.
More than 1,400 soldiers participated in a military parade called the Colonel's Review. Prince William was present at the ceremony, which served as a rehearsal for King Charles III's upcoming birthday celebration.
The soldiers wore traditional woolen tunics and bearskin hats while the temperature reached 86 degrees.