I reread my post and it isn't clear. The FDA warning not to take Metformin is for someone who currently has heart issues. No evidence a healthy person would develop heart issues by taking Metformin.
Further clarification is needed on the acronyms PAC's and PVC's as each has multiple definitions. If you meant current heart issues and/or potential heart issues, the FDA warns against taking Metformin as it could lead to fatal congestive heart failure.