Toxicity by antimonials has multiple systemic manifestations, including cardiovascular alteration, which is one of the most serious, as it can even lead to death of the patient. This article reports the case of an elderly patient who, during treatment with antimonials for cutaneous leishmaniasis, presented cardiac and hepatic toxicity associated with electrolyte imbalance as a perpetuating factor of her clinical condition, with subsequent development of multiple episodes of mono and polymorphic ventricular tachycardia. The patient was treated with synchronous and asynchronous defibrillation, overstimulation with pacemaker, and electrolyte replacement; she did not recover and eventually died. This report on the toxicity of antimonials is important as they remain the first-line treatment for leishmaniasis despite their multiple side effects, which can compromise multiple systems. Thus, health care professionals must become familiar with the early signs and symptoms of toxicity.