Functional medicine emphasises mechanisms, dynamic physiology, and the search for causes of dysfunction. In prenatal cardiology, an analogous approach means moving beyond the binary question of whether the fetal heart is structurally normal or abnormal and asking why fetal cardiovascular function has changed. The fetal heart is not only a target organ for diagnosing congenital heart disease; it is also an informational organ that reflects the haemodynamic environment created by the placenta, umbilical cord, fetal lungs, and maternal-fetal circulation. Functional fetal cardiac changes may occur in structurally normal hearts and may also modify the course and prognosis of congenital heart disease. They include cardiac enlargement, disproportion of chambers and great vessels, valvular regurgitation, abnormal Doppler flows, arrhythmias, impaired myocardial performance, pericardial effusion, and fetal heart failure. This narrative review presents functional fetal echocardiography as a pathophysiologic framework for prenatal cardiology. Particular attention is paid to three clinical models: placental thickening as a marker of fetal systemic stress, abnormal fetal/neonatal lung development manifested by a prenatal pattern of right heart pressure overload and pulmonary vascular maladaptation, and nuchal cord entanglement as a potential modifier of fetal streaming, myocardial performance, and pulmonary artery-aorta relationships. The review also proposes a practical algorithm and severity-weighted interpretation of functional fetal cardiac abnormalities. Functional echocardiography does not replace structural diagnosis; rather, it extends it by integrating cardiac anatomy, fetal circulation, extracardiac conditions, and the intrauterine environment into a single clinical interpretation.