Don't Miss the Warning Signs: Syncope Masquerading as a Major Congenital Heart Defect in a 42-Year-Old Patient.

Congenital heart defects (CHDs) are typically diagnosed in infancy, yet some may go unidentified until adulthood and pose significant clinical challenges. We present the case of a 42-year-old female patient with multiple CHDs, including sinus venosus atrial septal defect (ASD), partial anomalous pulmonary venous return (PAPVR), and moderate mitral regurgitation discovered incidentally after presenting to the emergency department with atypical chest pain. Initial warning signs were overlooked, and asymptomatic mitral valve prolapse (MVP) diagnosed in childhood had progressed into moderate mitral regurgitation due to lack of follow-up. Diagnostic workup, including transesophageal echocardiography (TEE), cardiac magnetic resonance imaging (MRI), and catheterization, revealed significant abnormalities requiring surgical intervention. This case highlights the importance of recognizing subtle warning signs, such as palpitations and unexplained fatigue, which may indicate underlying CHDs. Timely diagnosis and management are crucial in mitigating potentially life-threatening complications associated with undiagnosed CHDs in adults. Further research is needed to improve surveillance and treatment strategies for the growing population of adults with CHDs.