Lyme disease, caused by a tick-borne spirochete,Borrelia burgdorferi,is the most common vector-borne disease in the United States. Clinical manifestations can include erythema migrans, carditis, facial nerve palsy, or arthritis. A rare complication of Lyme disease is hemidiaphragmatic paralysis. The first case of this complication was documented in 1986, and since then, there have been 16 case reports associating hemidiaphragmatic paralysis with Lyme disease. This is a case of a patient found to be in atrial flutter likely resulting from left hemidiaphragmatic paralysis as a complication of Lyme disease. The patient was a 49-year-old male recently diagnosed with Lyme disease who was treated with a 10-day course of doxycycline and who presented with dyspnea and chest pain. He appeared in acute distress with tachypnea and tachycardia to 169 beats/minute but was not hypoxic. Electrocardiogram (EKG) showed atrial flutter with a rapid ventricular response (RVR). The patient was sent to the emergency department and was treated with intravenous (IV) metoprolol, followed by an IV diltiazem drip, and ultimately converted to normal sinus rhythm. Chest X-ray demonstrated an elevated left hemidiaphragm. Due to concern for Lyme carditis causing tachyarrhythmia, the patient was started on IV ceftriaxone 2 g daily. A transthoracic echocardiogram showed no valvular abnormalities and a normal ejection fraction, thus indicating a low likelihood of carditis. The patient was transitioned to oral doxycycline for an additional 17 days. During the hospital course, a fluoroscopic chest sniff test confirmed the left hemidiaphragmatic paralysis. A chest X-ray completed after two months showed persistent elevation of the left hemidiaphragm and the patient continued to have mild dyspnea. The main lesson from this case is to consider hemidiaphragmatic paralysis as a possible complication of Lyme disease.