from wiki:
Xanthines
Mate contains three xanthines: caffeine, theobromine and theophylline, the main xanthine being caffeine. Caffeine content varies between 0.7% and 1.7% of dry weight[14] (compared with 0.3–0.9% for tea leaves, 2.5-7.5% in guarana, and up to 3.2% for ground coffee)[15]; theobromine content varies from 0.3-0.9%; theophylline is present in small quantities, or can be completely absent.[16] A substance previously called "mateine" is a synonym for caffeine (like theine and guaranine)[17]
Studies of mate, though very limited, have shown preliminary evidence that the mate xanthine cocktail is different from other plants containing caffeine most significantly in its effects on muscle tissue, as opposed to those on the central nervous system, which are similar to those of other natural stimulants. The three xanthines present in mate have been shown to have a relaxing effect on smooth muscle tissue, and a stimulating effect on myocardial (heart) tissue.[18]
http://en.wikipedia.org/wiki/Yerba_mat%C3%A9#Chemical_composition_and_properties