Figure 50-28 Pressure-volume relationship of the pericardium in the presence of pericardial effusion. A, hyperacute cardiac tamponade (gunshot or stab wounds to the heart); B, subacute cardiac tamponade—the effusion developed over a period of a few days; C, effusion that has developed over a period of several weeks to months; D, chronic effusive pericarditis—pericardial pressure is slightly elevated but does not cause major hemodynamic impairment. (From Smith T: Cardiovascular Therapeutics: A Companion to Braunwald's Heart Disease. Philadelphia, WB Saunders, 1996, p 774.)