Figure 5.

The sodium pump of the cardiomyocyte is an energy consuming, Mg²⁺-dependent Na⁺/K⁺ ATPase which is responsible for the extrusion of three Na⁺ ions and entry of two K⁺ ions. Pump activity falters with Mg²⁺ deficiency accompanied by reduced intracellular K⁺ and prolongation of the QTc interval of the electrocardiogram. In the presence of hypokalaemia and hypomagnesaemia, digoxin, a Na⁺/K⁺ ATPase inhibitor, would further reduce intracellular K⁺ to raise the potential for arrhythmias.