A 4-year-old neutered female rottweiler underwent three separate anaesthetic events for the diagnosis and treatment of cranial cruciate ligament rupture. The patient was otherwise healthy, with consistently normal pre-anaesthetic electrolyte values. However, during the second anaesthetic procedure, the patient developed severe hyperkalaemia with life-threatening cardiovascular compromise. Prompt treatment led to rapid normalisation of plasma potassium levels and resolution of cardiac abnormalities. This case highlights the need for further research to elucidate the mechanisms underlying this rare but serious complication. Clinicians should remain vigilant, as intra-anaesthetic hyperkalaemia, though uncommon, can be fatal. While the condition has been historically associated with greyhounds, recently reported cases in rottweilers may warrant similar concern.