Respiratory changes in left ventricular inflow velocities by Doppler echocardiography have been used to assess cardiac tamponade; however, Doppler echocardiography has not been compared to right atrial or right ventricular collapse. Pulsed Doppler echocardiography of left ventricular inflow velocities was performed with respiratory monitoring in 28 patients with small to large pericardial effusions. Ten of the 17 patients (59%) with large effusions had equalization of right-sided diastolic pressures before pericardial drainage. The measurements performed included percent change in left ventricular inflow peak early velocity, isovolumic relaxation time, change in inferior vena cava diameter from apnea to inspiration, and the presence of right atrial and right ventricular collapse. Percent change in early left ventricular inflow velocities significantly correlated with pericardial effusion size (p = 0.001) and right ventricular collapse (p = 0.007), and showed a trend with right atrial collapse (p = 0.10). Pericardial effusions with a left ventricular inflow velocity change > 22% were found to have right-sided equalization at a 95% confidence interval. Our data indicate that the respiratory changes in Doppler echocardiographic parameters are useful in the assessment of pericardial effusion and tamponade. This study concurs with the hypothesis that there is a continuum of hemodynamic compromise in pericardial effusion that is easily detected by Doppler echocardiography.