A (1) Pericardial fluid (blue) bathes the normal heart including the (2) right and (3) left atria. Green arrows represent atrial conduction. B Surgery disrupts the pericardium and blood and inflammatory cells enter the pericardial space (4). C (1) Pericardial fluid composition now includes inflammatory cells, cytokines, and highly oxidative proteins, causing atrial fibrillation (green arrows).