A gated blood-pool equilibrium radionuclide angiography was performed in a patient to determine the ejection fraction for doxorubicin cardiotoxicity evaluation. The phase image of the first harmonic of the Fourier analysis revealed a severe delay of the right ventricular contraction compared with that of the left ventricle. This right ventricular contraction asynchronism was due to a large pericardial effusion, confirmed by the presence of the halo sign on the summed gated images and by echocardiography. The phase delay moves towards normalization after pericardiocentesis. Although radionuclide angiocardiography is not the best method for identification of pericardial effusion, this diagnosis should be evoked when a severe homogenous delay of the right ventricular contraction is observed.