An elderly man presented with general lethargy and reduced exercise tolerance
Surrounding the heart is a pericardial effusion (the anechoic space). There is both right atrial and right ventricular collapse, which disappears during inspiration.
RA and RV collapse are signs of tamponade. This often results in a see - saw or serpiginous appearance of the right side of the heart, as the chambers collapse at different stages of the cardiac cycle. Note that RA contraction is normal, but if the wall bends 'into' the atrium, it is collapsing.
Since this is only occurring during expiration, the pericardial pressure is not much greater than the right sided intracardiac pressures. As a result, once the patient was given a small volume of fluid (increasing his venous pressures) his condition improved and the collapse disappeared.
See a further example and discussion of tamponade in case 1 http://www.ultrasoundvillage.com/imagelibrary/cases/?id=103
Video player will go here
Note the collapse of the RA and RV