eng Science and Education Publishing American Journal of Medical Case Reports 2374-216X 2025-08-22 13 7 41 45 10.12691/ajmcr-13-7-2 AJMCR20251372 article Resha Reya Ganthan MD reshareya15@gmail.com 1 Fadi Yacoub MD 2 Asher Gorantla MD 2 Nidal Isber MD FACC FHRS 3 4 Department of Internal Medicine, Richmond University Medical Center/Mount Sinai, Staten Island, NY, USA Department of Cardiology, State University of New York Downstate, Brooklyn, NY, USA Department of Cardiology, Richmond University Medical Center/Mount Sinai, Staten Island, NY, USA The long-term effects following a COVID-19 infection vary widely, with that including inappropriate sinus tachycardia as a manifestation. Herein we report the case of a middle-aged woman with a history significant for a COVID-19 infection 2-years prior, following which she developed brief episodes of palpitations, otherwise controlled with Metoprolol Succinate. She presented to the hospital after a 1-week history of worsening palpitations far worse in severity from prior episodes, associated with shortness of breath and pre-syncope. ECG on admission demonstrated sinus tachycardia with a significantly elevated heart rate. Multiple repeat ECGs demonstrated periods of sinus tachycardia when symptomatic alternating with a normal sinus rhythm when asymptomatic. Continuous telemetry monitoring while inpatient reported similar findings, with no other tachyarrhythmias present. Multiple other diagnostic tests were performed to rule out a more malignant cause of autonomic instability, which ultimately yielded negative results. The patient was however additionally diagnosed with orthostatic hypotension, which posed a potential confounding factor in the steadfast diagnosis of inappropriate sinus tachycardia. This case highlights the multiple simultaneous manifestations of post-covid syndrome with significant symptom overlap, leading to a missed diagnosis. https://pubs.sciepub.com/ajmcr/13/7/2/ajmcr-13-7-2.pdf Inappropriate sinus tachycardia (IST) Intrinsic heart rate (IHR) Electrocardigram (EKG) Orthostatic hypotension Post-Covid syndrome (PCS) Postural orthostatic tachycardia syndrome (POTS) Sinoatrial node (SAN) Transthoracic echocardiography (TTE) Tilt-table test (TTT)