Congenital heart disease can be difficult to diagnose in infants because they often present with nonspecific symptoms. Their clinical presentation can resemble that of respiratory infections or sepsis, yet typical treatments for these conditions such as fluid resuscitation may worsen their course. We report a case of an 8-week-old boy who had several weeks of viral symptoms and eventually presented to the emergency department in shock. An echocardiogram revealed the diagnosis of cor triatriatum, a rare congenital heart disease that requires urgent surgical repair. In this article, we review the evaluation and management of such patients and emphasize the importance of considering congenital heart disease in the differential diagnosis for an infant in shock.