The optimal approach towards managing serum potassium and hemodialysate potassium concentrations is uncertain. To study this, adults receiving hemodialysis for three months or more with hyperkalemia (pre-dialysis serum potassium (sK+) 5.1–6.5 mEq/l) had cardiac monitors implanted and were randomized to either eight weeks of 2.0 potassium/2.5 calcium mEq/l dialysate without sodium zirconium cyclosilicate (SZC) (2.0 potassium/noSZC) or 3.0 potassium/2.5 calcium mEq/l dialysate combined with SZC (3.0 potassium/SZC) on non-dialysis days to maintain pre-dialysis sK+ 4.0–5.5 mEq/l, followed by treatment crossover for another eight weeks.