While the reduced basal NCX function in hetKO led to a phenotype with reduced likelihood of arrhythmia and a balanced Ca2+ homeostasis as reported previously (Bögeholz et al., 2015), lowering NCX function below this level with SEA0400 was clearly detrimental in hetKO, WThetKO, and WTOE. The gene discussed is TLX2; the disease is cardiac arrhythmia.