A  

In constrictive pericarditis, restrictive cardiomyopathy and severe tricuspid regurgitation the right ventricle empties the right atrium abruptly in early diastole, producing a steep (deep) y-descent on the JVP tracing.  In cardiac tamponade pericardial pressure limits early ventricular filling, so the y-descent is classically absent or markedly blunted, not deep [Kearns MJ 2018 PMID 29137910; Wise DE 1976 PMID 1000537; Cha SD 1982 PMID 7140400].