Lyme Carditis: A Reversible Culprit in Non-Ischemic Cardiomyopathy.

Lyme disease (LD), caused by , is a tick-borne illness that can lead to Lyme carditis, which most commonly presents as a high-degree atrioventricular (AV) block. While conduction abnormalities are well-documented, LD has also been implicated in non-ischemic cardiomyopathy, though this manifestation remains rare and under-recognized. We present the case of a 57-year-old female with newly diagnosed heart failure with reduced ejection fraction (HFrEF) and first-degree AV block, who initially presented with nausea, dizziness, fatigue, and gastrointestinal symptoms. Her history included multiple tick bites, subacute joint pain, and intermittent nonspecific rashes. Initial transthoracic echocardiography (TTE) demonstrated severe global hypokinesis with a left ventricular ejection fraction (LVEF) of 10-15%. Extensive ischemic and inflammatory workups, including coronary angiography and cardiac MRI, were unremarkable. However, Lyme serology was positive, and the patient was started on a 21-day course of doxycycline alongside guideline-directed heart failure therapy. A follow-up TTE months later demonstrated remarkable recovery, with LVEF improving to 55-59% and resolution of wall motion abnormalities. This case highlights the importance of considering LD as a reversible cause of non-ischemic cardiomyopathy, particularly in patients with risk factors such as tick exposure and relevant clinical symptoms. Early recognition and appropriate antimicrobial treatment can lead to significant cardiac recovery, underscoring the need for a high index of suspicion when evaluating new-onset systolic dysfunction with an otherwise negative ischemic workup.