Every cell in the body needs magnesium. It helps keep muscles strong and nerves alert. And a new study in the journal Circulation suggests that daily magnesium supplements can even help an ailing heart. Lead author C. Noel Bairey Merz, MD, Director of the Preventive and Rehabilitative Cardiac Center at Cedars-Sinai Medical Center in Los Angeles, says that magnesium supplements enabled heart disease patients to exercise for longer periods and appeared to protect their hearts from the stress of exercise. Patients who took magnesium had better blood vessel function and their hearts showed less stress during treadmill exercise compared to the placebo group.