We examined the Atlantic surfclam (Spisula solidissima) transcriptome under heat stress and assessed how a selective pressure could alter the gene expression profile of a surfclam population. We utilized two groups of clams, one which had been selected for greater heat tolerance via an acute heat stress four months prior to the study, and a group of randomly-selected control clams that never experienced severe heat stress. After a six-hour exposure to 16 or 29C, we compared the transcriptome expression profiles of the four temperature/group combinations.