The Heterothalamus brunioides Less is a native plant of Santaninha region of Boa Vista (RS) and utlizado in folk medicine to alleviate the toxic effects produced by snake bites. The objective was to study the lethal dose as well as the effects of the aqueous extract of this plant on the general activity and central nervous system in Wistar rats. The lethal dose was 143.2 mg / kg of the cold aqueous extract and, when boiled, the toxic effects disappeared, so it is thermolabile. In general activity did not present any signs that could be contraindicated the use. Its effect on the central nervous system is characterized by depression.
