Pericardial Disease in Dogs
The heart is a muscular pump that pushes blood throughout the entire body. In a normal dog, it beats approximately 150,000 times a day. The pericardium is a membrane that envelopes the heart. It has two layers: a thin, inner layer that adheres to the heart muscle, and a thicker outer layer that is a fibrous, rather tough sac. The space between the two layers, called the “pericardial space,” normally contains a small amount of fluid. If the fluid accumulates in the pericardial space to such an extent that it prohibits the heart from pumping properly, heart disease and even failure can result.
The heart has four chambers, as shown in the illustration below. Like many mechanical pumps, the heart has two functional parts. The atria, which are the thin-walled chambers labeled “left atrium” and “right atrium,” act as pump primers. Blood returning to the heart is held here and, when the atria are full, they contract, pushing blood into the pumping chambers or ventricles. When full, these pumping chambers contract forcefully, pushing blood out to all the blood vessels in the body.
You’ll see that the heart is actually made up of two pumps, labeled right and left, based on their anatomic position in the body. So we have one pump made up of the right atrium and right ventricle and one made up of the left atrium and left ventricle. Valves between the atrium and the ventricle ensure blood always moves in one direction, from the atrium into the ventricle. The heart is made up of two pumps because our pets’ bodies, like ours, have two different circuits for blood flow, moving first through one and then the other. One of these circuits takes blood through the lungs so that oxygen can be replenished and waste gases, like carbon dioxide, are removed. This oxygen-enriched blood then moves through the other circuit, reaching all parts of the body to deliver the oxygen needed for normal body function and removing any waste products produced as a consequence.
So long as it is healthy, the pericardium has no real effect on basic heart function other than providing protection and lubrication. When diseased, however, it can have a significant influence and cause severe, sometimes life-threatening conditions. The most common conditions that affect the pericardium are inflammation and cancer. Either one of these problems can lead to excessive production of fluid within the