<qa>  What is the primary endpoint of the study?To evaluate the primary objective, the Investigator will conduct a double-blind randomized trial assigning participants to receive 400 mg of oral magnesium in the form of magnesium citrate once daily or placebo. The investigators will recruit 60 individuals 55 years of age and older without a prior history of cardiovascular disease. At baseline, participants will undergo a basic examination, answer questionnaires and provide a blood sample to determine circulating magnesium levels. Participants will then wear an FDA-approved heart rhythm monitor Zio XT Patch for 2 weeks. At the end of 2 weeks they will begin taking their assigned treatment magnesium or placebo, and will continue doing so for a total of 12 weeks through study week 14. After 10 weeks of taking the supplement or placebo study week 12, they will have a final study visit in which the participants will provide another blood sample for assessment of circulating magnesium, and will be asked to wear the heart rhythm monitor for another 2 weeks through study week 14. The primary endpoint will be the change in burden of premature atrial contractions PACs, measured in episodes per day, between baseline and final follow-up visit. A secondary outcome will be the change in circulating magnesium between both exams. 