Signs of pericardial tamponade include tachycardia, pulsus paradoxus, elevated jugular venous pressure, and hypotension; however, some patients may develop tamponade without this clinical pattern.
A chest x-ray may show widening of the cardiac silhouette  if the amount of pericardial fluid collection exceeds 250 cc; however, a chest x-ray cannot determine the degree of cardiac dysfunction or tamponade. Loculated pericardial effusions may not be apparent on standard posterior/anterior or lateral chest radiographic views.
Transthoracic echocardiography using apical, subxiphoid, and parasternal views can evaluate the presence, quantity, and quality of suspected pericardial effusions as well as associated pericardial masses and inflammation. Moderate effusions on echocardiography show an echo-free space of 10 mm to 20 mm during diastole in M-mode or 2-dimensional echocardiography, whereas severe effusions have an echo-free space exceeding 20 mm.[21,22] Echocardiography can also determine right and left ventricular function and the possibility of right ventricular or atrial diastolic collapse. Left ventricular collapse caused by large pleural effusion without clinically significant pericardial effusions has been reported;[4,16,23,24] however, transesophageal echocardiography may be useful for loculated effusions resulting from adhesions adjacent to the atria, where the thinness of the atrial wall may not be well visualized on transthoracic echocardiography.[4,16]
Echocardiography in pericardial effusion with tamponade shows right atrial or right ventricular compression, or left atrial compression, decreased left ventricular dimension, and absence of collapse of the inferior vena cava on deep inspiration.[6,25] Echocardiography findings predictive of pericardial tamponade have been reported. Right atrial collapse has a sensitivity of 55% to 60% and a specificity of 50% to 68%. Right ventricular diastolic collapse has a lower sensitivity of 38% to 48% but a higher specificity ranging from 84% to 100%. Because neither finding provides 100% sensitivity and specificity, patients who are clinically symptomatic should have a diagnostic pericardiocentesis, even in the absence of definitive findings on echocardiography.[4,27] One study found right atrial collapse present in only 42% of patients and right ventricular collapse in 62%. Nonetheless, 80% of patients with malignant pericardial effusions had symptomatic relief following pericardiocentesis.