Septal bounce is a sign of ventricular interdependence on echocardiography, cardiac CT, and cardiac MRI, manifested by paradoxical interventricular septal movement during early diastole (i.e. initial septal movement towards and then away from the left ventricle) seen mainly in constrictive pericarditis and occasionally cardiac tamponade.
When motion of the ventricular walls is decreased (e.g. tethered by the pericardium or from the pressure of pericardial fluid), the volume of the heart is effectively fixed. Changes in ventricular volumes and pressures in early diastole are then reflected through deviations of the septum.
Septal bounce is a specific and relatively sensitive sign of ventricular interdependence due to constrictive pericarditis and is considered a reliable sign to distinguish constrictive pericarditis from restrictive cardiomyopathy.