Inappropriate ICD shocks remain a common problem. Double counting of single ventricular events can occur with biventricular ICDs implanted before univentricular sensing was available. Often this is due to a tachyarrhythmia or loss of left ventricular capture. This report describes a patient who developed hyperkalemia during hemodialysis, received inappropriate ICD shocks and experienced loss of biventricular pacing due to T wave rather than QRS double counting. Oversensing was abolished by reducing the potassium content of the dialysis bath. This underscores the need for careful interpretation of saved electrograms to determine the cause for, and appropriate treatment of, device related problems.