What Causes Intermittent Low-Grade Fever and Palpitations?

Intermittent low-grade fever accompanied by palpitations can signal a range of underlying conditions—some benign, others requiring prompt medical evaluation. A low-grade fever is typically defined as a persistent or recurrent temperature between 37.5°C and 38.3°C (99.5°F–100.9°F), while palpitations refer to the subjective sensation of a rapid, fluttering, or pounding heartbeat.

Common non-cardiac causes include chronic infections such as latent tuberculosis, brucellosis, or endocarditis—particularly if valvular abnormalities are present. Autoimmune disorders like systemic lupus erythematosus (SLE), rheumatoid arthritis, or vasculitides may also manifest with subfebrile temperatures and autonomic dysregulation leading to palpitations. Thyroid dysfunction—especially subclinical or overt hyperthyroidism—is another frequent contributor, as excess thyroid hormone increases cardiac output and metabolic rate.

Cardiovascular etiologies warrant careful assessment: arrhythmias such as atrial fibrillation or supraventricular tachycardia may present with palpitations and low-grade inflammation; heart failure with preserved ejection fraction (HFpEF) can sometimes feature subtle febrile responses due to systemic inflammation. Less commonly, malignancies—including lymphomas and leukemias—may cause paraneoplastic fever and catecholamine-mediated tachycardia.

Other considerations include medication side effects (e.g., bronchodilators, decongestants, certain antidepressants), anxiety disorders with physiological hyperarousal, and chronic fatigue syndrome/myalgic encephalomyelitis (ME/CFS), where immune dysregulation and autonomic nervous system imbalance coexist.

Clinical evaluation should include a detailed history (duration, triggers, associated symptoms such as weight loss, night sweats, joint pain, or fatigue), physical examination focusing on vital signs, cardiac auscultation, lymphadenopathy, and thyroid assessment, followed by targeted investigations: complete blood count, inflammatory markers (ESR, CRP), thyroid function tests, blood cultures, chest imaging, and electrocardiography. Echocardiography may be indicated if structural heart disease or endocarditis is suspected.

Because this symptom combination crosses multiple organ systems, timely multidisciplinary assessment—often involving internal medicine, cardiology, and rheumatology—is essential to identify treatable causes and prevent diagnostic delay.