An image showing a hemopericardium, which is where blood collects in the pericardium sac that encases the heart. In this particular case it was caused by an aortic dissection - which is when there is a tear in the wall of the aorta. An aortic dissection may lead to hemopericardium when blood dissects through the media proximally. Such a massive amount of hemorrhage can lead to cardiac tamponade.