In constrictive pericarditis, which physical examination finding is most characteristic?

• A. Pericardial knock
• B. Displaced point of maximal impulse
• C. Muffled heart sounds
• D. S3 gallop

Answer: (A)

In constrictive pericarditis, the noncompliant, thickened pericardium abruptly halts the rapid early diastolic filling of the ventricle. This creates a distinct early diastolic sound—the pericardial knock—that occurs a short time after S2 and is best heard along the left lower sternal border. It reflects the sudden cessation of ventricular filling due to the rigid pericardium, a hallmark feature of constriction.

Other findings don’t fit this scenario as well. A displaced point of maximal impulse suggests altered chamber size or function but isn’t specific to constriction. Muffled heart sounds point more toward pericardial effusion and tamponade. An S3 gallop arises from volume overload and dilated ventricles, typical of systolic heart failure, not constrictive physiology. The pericardial knock uniquely captures the rapid early diastolic filling followed by abrupt stoppage caused by a noncompliant pericardium, making it the most characteristic finding.