The normal pericardial sac contains the heart along with a trace volume of fluid. When excess fluid accumulates the heart may get squashed, impairing filling and pumping. When there is a lot of fluid, the heart also becomes mobile. The ECG tracing, taken from stickers on the skin, might show variability due to the simple fact that the heart is essentially swimming in a massive volume of fluid and moving about quite considerably. This particular patient has an enormous pericardial effusion, which had been building up slowly over years. The ECG in the centre is taken from Ed Burns's peerless ECG Library on the incredible Life in the Fast Lane.