Pericardial effusion with constrictive physiology describes a condition in which the pericardial fluid and thickened and dense pericardium limit left ventricular (LV) diastolic filling and prevent ventricular stretch. This leads to equalization of the end-diastolic pressure in cardiac chambers and poor ventricular filling. We report two patients, who presented with symptoms and signs of severe heart failure and with significantly raised BNP levels who were subsequently diagnosed to have pericardial effusion with constrictive physiology. When VATS pericardial window procedure was performed, the BNP values transiently increased even more in both patients, and returned to pre-operative levels at 5 days post-op. We therefore propose that in contrast to current evidence, grossly elevated BNP levels can coexist with a diagnosis of constrictive pathology. Further studies into constrictive pericarditis should take into account the transient changes in BNP observed in our study that may reveal more regarding the pathophysiology of constrictive pericarditis.