An eleven-year-old, domestic short haired cat presented out-of-hours with a one-day history of dyspnoea and open-mouthed breathing. Ninety minutes after arrival the cat acutely deteriorated. Butorphanol (0.2 mg/kg) was administered intravenously via a pre-placed cephalic vein cannula, after which anaesthesia was induced (1.3 mg/kg alfaxalone). The cat’s trachea was intubated with a 3.5 mm internal diameter cuffed endotracheal tube (ETT) but it was not possible to give a manual breath and a capnograph trace was absent; therefore the ETT was replaced with a 4.5 mm internal diameter cuffed ETT. A manual breath was still not possible but a capnograph trace was present [end-tidal CO2 tension of 95 mmHg (12.7 kPa)]. Intravenous dexamethasone (0.15 mg/kg) and terbutaline (0.01 mg/kg) were administered. Computed tomography revealed a heart base mass compressing the trachea and decreasing its lumen to 1 mm diameter. The cat was euthanised due to poor prognosis. Histopathology revealed a chemodectoma.