Three tomato (Solanum lycopersicum) cultivars [Walter LA3465 (heat-tolerant), Edkawi LA 2711 (unknown heat tolerance, salt-tolerant), and LA1310 (cherry tomato)] were compared for changes in leaf proteomes after heat treatment. Seedlings with four fully expanded leaves were subjected to heat treatment of 39/25 °C at a 16:8 h light–dark cycle for 7 days. Leaves were collected at 1200 hr, 4 h after the light cycle started. For ‘Walter’ LA3465, heat-suppressed proteins were geranylgeranyl reductase, ferredoxin-NADP (+) reductase, Rubisco activase, transketolase, phosphoglycerate kinase precursor, fructose–bisphosphate aldolase, glyoxisomal malate dehydrogenase, catalase, S-adenosyl-L-homocysteine hydrolase, and methionine synthase. Two enzymes were induced, cytosolic NADP-malic enzyme and superoxide dismutase. For ‘Edkawi’ LA2711, nine enzymes were suppressed: ferredoxin-NADP (+) reductase, Rubisco activase, S-adenosylmethionine synthetase, methioine synthase, glyoxisomal malate dehydrogenase, enolase, flavonol synthase, M1 family peptidase, and dihydrolipoamide dehydrogenase. Heat-induced proteins were cyclophilin, fructose-1,6-bisphosphate aldolase, transketolase, phosphoglycolate phosphatase, ATPase, photosystem II oxygen-evolving complex 23, and NAD-dependent epimerase/dehydratase. For cherry tomato LA1310, heat-suppressed proteins were aminotransferase, S-adenosyl-L-homocysteine hydrolase, L-ascorbate peroxidase, lactoylglutathione lyase, and Rubisco activase. Heat-induced enzymes were glyoxisomal malate dehydrogenase, phosphoribulokinasee, and ATP synthase. This research resulted in the identification of proteins that were induced/repressed in all tomato cultivars evaluated (e.g., Rubisco activase, methionine synthase, adenosyl-L-homocysteine hydrolase, and others) and those differentially expressed (e.g., transketolase).