pericardial knock

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per·i·car·di·al knock

an early diastolic sound that is a variant of the third heart sound, but occurring distinctly earlier, due to rapid ventricular filling's being abruptly halted by the restricting pericardium; a true "knocking" quality is uncommon.
Farlex Partner Medical Dictionary © Farlex 2012

pericardial 'knock'

Cardiology A loud 3rd heart sound occurring when the ventricular filling abruptly stops at the end of the early diastolic pressure dip–ie, at the end of the rapidly filling phase of the ventricles; classically associated with severe constrictive pericarditis, or with penetrating trauma to the pericardium, the PK has a relatively high pitch, often ↑ in intensity with inspiration and coincides with the nadir of the 'y' descent of the jugular venous pulse, resembling a premature 3rd sound. Cf Gallop.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.