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Objectives. This study was designed to describe the hemodynamic abnormalities associated with the appearance of left ventricular diastolic collapse in the setting of regional left heart cardiac tamponade.Background. Cardiac tamponade after heart surgery is frequently associated with localized pericardial effusion. Although right ventricular diastolic collapse and right atrial collapse are reliable echocardiographic findings in patients with circumferential pericardial effusion and tamponade, they are often not present in postoperative patients with localized pericardial effusion and regional left heart tamponade. Left ventricular diastolic collapse has been described in such patients, but the degree of hemodynamic alteration that exists with this finding is not known.Methods. Acute regional left heart tamponade was produced 14 times in seven spontaneously breathing anesthetized dogs by infusing fluid into an isolated compartment created in the pericardial space adjacent to the left ventricular free wall. Continuous echocardiographic imaging and hemodynamic monitoring of left ventricular, systemic arterial, right atrial, pulmonary capillary wedge and pericardial pressures were performed. Measurements at baseline were compared with those made at the onset of left ventricular diastolic collapse and at decompensated tamponade.Results. Left ventricular diastolic collapse was noted in all 14 episodes of regional tamponade. It occurred when pressure in the left pericardial compartment exceeded left ventricular diastolic pressure by 3.0 ± 1.9 mm Hg. At the onset of left ventricular diastolic collapse, cardiac output and mean arterial pressure were significantly reduced from the control value (p < 0.05). Systolic hypotension was noted only twice at this stage, respiratory variation in systolic pressure > 10 mm Hg only once. The appearance of this sign was also associated with elevated left heart filling pressures.Conclusions. Left ventricular diastolic collapse is a reliable sign of regional left ventricular tamponade and is associated with a reduction in cardiac output. This echocardiographic finding usually occurs before the development of arterial hypotension and pulsus paradoxus. Thus, left ventricular diastolic collapse is potentially more reliable than hypotension or pulsus paradoxus in the diagnosis of regional left ventricular tamponade.