In the apical 4-chamber view from a patient with a small pericardial effusion (pe), the pe is seen best behind and above the RA, which is the most sensitive area for detecting small effusions. In larger pe, the RA collapses at this point, providing a highly sensitive, but minimally specific sign of cardiac tamponade.
LA: left atrium; LV: left ventricle; PE: pericardial effusion; RA: right atrium; RV: right ventricle.