To determine the hemodynamic derangement associated with right ventricular diastolic collapse and to assess the value of right ventricular and right atrial collapse in identifying cardiac tamponade, two-dimensional echocardiograms were recorded simultaneously with measurement of right atrial, pulmonary capillary wedge, intrapericardial, and systemic arterial pressures and cardiac output in 16 patients as they underwent pericardiocentesis. Twelve patients (group I) had evidence of right ventricular or right atrial collapse or both on their echocardiograms and hemodynamic evidence of cardiac tamponade before pericardiocentesis. All hemodynamic parameters improved after pericardiocentesis (p less than or equal to .05). Continuous monitoring during pericardiocentesis in three of these patients showed significant improvement in all parameters except heart rate (p less than or equal to .02) at the point of disappearance of right ventricular diastolic collapse, with further improvement in cardiac output as pericardiocentesis continued (p less than .01). Right atrial collapse persisted after right ventricular collapse disappeared but was no longer present when pericardiocentesis was completed. Three patients (group II) had no right ventricular or right atrial collapse, no hemodynamic evidence of cardiac tamponade, and no improvement in hemodynamic parameters after pericardiocentesis. A single patient (group III) was found to have elevated right heart pressures and right ventricular hypertrophy before pericardiocentesis. Although there was hemodynamic evidence of cardiac tamponade in this patient, there was no evidence of right ventricular or right atrial collapse. In this study, the sensitivity of right ventricular collapse as a marker for cardiac tamponade was 92%, its specificity 100%, its accuracy 94%, and its predictive value 100%.(ABSTRACT TRUNCATED AT 250 WORDS)