No evidence exists that adjusting the fluoride content of public water supplies to a level of about one part per million has any harmful effect on the cardiovascular system.
The possibility that magnesium deficiency has a role in the development of coronary heart disease is only an interesting and provocative hypothesis. That won't change until there's better resolution of the apparent epidemiological (ep"e-de"me-o-LOJ'ih-kl) inconsistencies and perhaps more complete knowledge about the human magnesium requirement.
A number of trace elements have been implicated as possible contributors to cardiovascular disease. Zinc, copper, cadmium and lead, individually or in combination, are probably more biologically plausible than others. Still, there's little evidence to make any definitive statement even on these elements, let alone draw any conclusions about their role in the development of coronary heart disease.
Whether there's a relationship between the quality of drinking water and cardiovascular health hasn't been resolved. Until more studies are done on this, no definitive conclusions can be drawn. Some sources of water are very high in sodium. People with high blood pressure should avoid drinking water that's high in sodium.