Typical Symptoms of Myocarditis in Infants

Infants with myocarditis often present with nonspecific, subtle signs that can easily be mistaken for common viral illnesses. Key clinical manifestations include tachypnea (rapid breathing), poor feeding or decreased oral intake, lethargy, irritability, and failure to thrive. Many affected infants develop signs of heart failure—such as tachycardia out of proportion to fever, gallop rhythm, hepatomegaly, and peripheral edema—though these may be muted or delayed in very young patients. Fever is frequently absent, even in cases with an infectious etiology. In severe presentations, infants may exhibit pallor, cyanosis, hypotonia, or sudden hemodynamic collapse due to acute left ventricular dysfunction or arrhythmias. Because diagnostic imaging and biomarker interpretation are challenging in this age group—and because symptoms overlap significantly with sepsis, bronchiolitis, or metabolic disorders—myocarditis should remain a high-index differential in any infant with unexplained respiratory distress, cardiovascular instability, or progressive lethargy.