Cardiac tamponade.

Hemodynamic abnormalities induced by pericardial effusion can be categorized by stages. During phase I, pericardial and left and right ventricular pressures are elevated but not equilibrated, and cardiac output is not compromised. During phase II, elevated pericardial and right ventricular filling pressures are equilibrated with each other but not with left ventricular filling pressure, which is higher. Cardiac output is compromised, and pulsus paradoxus is present in most but not all patients. During phase III, elevated pericardial right ventricular and left ventricular filling pressures are equilibrated, cardiac output is severely compromised, and pulsus paradoxus is present in all patients.