Which condition is most plausible based on the finding indicated by the arrow on this...

The image is a parasternal long axis M-mode echocardiographic tracing demonstrating the interventricular septum and posterior left ventricular wall. The arrow points to the septal “bounce” or “shudder,” which is an abnormal early diastolic septal motion.

This septal bounce is a classic echocardiographic finding in constrictive pericarditis, caused by rapid early diastolic filling with abrupt cessation due to pericardial constraint, resulting in paradoxical septal motion.

Cardiac tamponade usually shows pericardial effusion with chamber collapse but not septal bounce. Pulmonary embolism and pulmonary hypertension have different echocardiographic signs such as right ventricular dilatation and pressure overload but no septal bounce.

These features are well described in the "Textbook of Clinical Echocardiography" and ASE pericardial disease guidelines【16:Textbook of Clinical Echocardiography, 6e†p.280-285】【12:ASE Pericardial Disease Guidelines†p.300-305】.