SUMMARY1. Intravenous injections of quazodine (6,7‐dimethoxy‐4‐ethylquinazoline, 0–5 mg/kg per min) in pentobarbitone‐anaesthetized cats increased heart rate, the maximum rate of pressure development in the left ventricle (LV dP/dt max.), cardiac output and myocardial blood flow, and decreased systemic arterial blood pressure. The effects of this cardiac stimulant were examined 1, 2, and 3 h after the intravenous administration of 2 mg/kg ofE. coliendotoxin.2. During the endotoxin shock phase (>1 h after endotoxin) the most pronounced effects were decreases in systemic blood pressure and cardiac output and a severe metabolic acidosis.3. Quazodine failed to increase cardiac output during endotoxin shock and the effects on the heart rate and LV dp/dt max. were much reduced. In contrast, quazodine‐induced vasodilatation was much more marked.4. It is concluded that there is profound myocardial depression in severe endotoxin shock in the cat and that this cannot be significantly modified b