Hi Welcome to HCM. I appreciate your concern for the safety of Botox injection when used for cosmetic purpose. It is unfortunate that you had to have this harmful side effect. Yes, Inj Botox can cause cardiac arrhythmia Potential and the most common side effects of Inj Botox include: Pain at the injection site, infection, inflammation, swelling, redness, bleeding and bruising. Other less common but serious side effects include: Cardiac arrhythmias which can be fatal, generalized muscle weakness, blurring of vision, difficulty in swallowing and speech, urinary incontinence and breathing difficulties. These symptoms have been reported hours to weeks after injection. The exact relationship of cardiac arrhythmia to the injection Botox has not been established. Hope these clarifications have answered your query. Wishing you best of your health.