Magnesium and potassium content of normal heart muscle in areas of hard and soft water.

Concentrations of both magnesium and potassium were significantly increased in normal heart muscle samples from an area with a soft water supply compared with matched samples from an area with hard water. The zinc contrentration was also slightly increased in the soft water area. The magnesium/potassium ratio was significantly lower in the softwater area. This relative deficiency of magnesium may increase the risk of death after myocardial infarction in soft-water areas.