Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Its prevalence in cancer patients undergoing treatment with radiation or chemotherapeutic agents has been on the rise. The most common offending agents are alkylating agents and anthracyclines causing various types of arrhythmias, including AF. We report a case of a 62-year-old male who was diagnosed with stage IV pleomorphic rhabdomyosarcoma and was started on chemotherapy with a mesna-ifosfamide and doxorubicin (MAI) regimen. He developed AF with a rapid ventricular rate soon after his second cycle of treatment, which got better with the initiation of beta-blocker therapy. Since low blood counts, including low platelet levels, are expected in patients with chemotherapy, the continual use of anticoagulation therapy varies on a case-to-case basis.