From all I have learned magnesium being too low can cause a heart attack. Mag relaxes muscles. Calcium tightens them. I have read this on medical/Dr sites.
If I don't take mine I have chest pains, muscle spasms all over, and ache more. If someone poops too much from mag though I was told by a DR mag glycinate or malate is best.
Malate form many with fibromyalgia take. Hope this helps.