In addition to Octavius' confident explanation; it helps to know that the heart is contained within a sack, called the pericardium. This sack or membrane has an inner and outer layer, with a small amount of lubricating fluid in between. The fluid content can increase for various reasons, aften related to inadequate respiration and the bodies inability to give off water (as in emphysema patients, for example). As the fluid builds it resricts the heart, making it work harder. This can cause, if untreated, an enlargement of the heart. Paradoxically, though the heart is enlarged it becomes less and less efficient resulting in the aforesaid congestive heart failure. The "congestive" in the title relates to the failure, generally, of one of the chambers of the heart not emptying adequately when filled by the other chambers, hence it becomes congested....