1. There is no known cause for the increased mortality due to ischaemic heart disease in soft water areas. Since the lead concentration of soft water is elevated in houses with lead plumbing, studies have been carried out to determine the effects of lead on the heart of rats.

2. Rats were given drinking water containing lead for 1 year at concentrations similar to those found previously in Glasgow, which has a soft water supply.

3. There was increasing deposition of lead in the heart and a fall in the cardiac levels of the enzymes ferrochelatase and δ-aminolaevulinic acid dehydratase. These changes are maximal after 6 months, when there were marked electron-microscopic changes in the myocardium and myocardial mitochondria.

4. Further studies are needed to determine whether lead is a cause of the increased mortality from ischaemic heart disease in soft water areas.

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