The pericardium is a double-layered sac that surrounds the heart; the visceral (that is in contact with the heart) pericardium is a serous membrane that is separated by a small quantity (15–50 mL) of fluid, from the fibrous parietal pericardium. Pericardial effusion is defined as an abnormal accumulation of fluid in this cavity.
If the effusion is small, there may be no symptoms as all, but as it accumulates the patients begin to have symptoms of dyspnea, that worsens over time, with an associated tachycardia. There may be symptoms of chest pain that is relieved on leaning forward. Some patients may report lightheadedness with syncope or near syncope. Symptomatic patients usually have evidence of right side heart compromise that may be assessed on echocardiography.
On examining the patient, there may be the classic triad of hypotension, decreased heart sounds and signs of increased jugular venous distension. There may be a pericardial friction rub and a positive hepatojugular rub. Pulsus paradoxus may occur which is defined as a drop of the systolic blood pressure of more than 10mmHg on inspiration due to falling cardiac output. Ewarts sign (Dullness to percussion under the angle of the left scapula) may be positive .
Initial workup will include an electrocardiogram which may show:
A chest X-ray may show an enlarged globular heart. Echocardiogram is the most sensitive test for pericardial effusion and will also provide information about the estimated amount, the function of the ventricle and if they have been compromised by the effusion. The effusions are graded as mild (50-100mls), moderate (100-500mls) and severe (>500mls).
Establishing the cause is important in symptomatic effusions. This will entail ruling out the causes as listed in the etiology section and will require echocardiogram assisted pericardial effusion aspiration. The fluid is sent for the relevant tests for the underlying cause to be identified. MRI and CT Scan may be used to access the presence of effusion .
Symptomatic effusion requires aspiration of the fluid, pericardiocentesis, and this may be done with ultrasound or echocardiogram guidance with drainage insertion. Pericardiocentesis has to be done rapidly in patients with compromised hemodynamics. Treatment of underlying causes such as tuberculosis is required to prevent reaccumulation   .
The outcome is highly dependent on the cause. Most patients with acute pericarditis present with minimal effusions and many will have a self-limiting course. Viral causes as well are usually self-limiting and will heal with no long term complication. Other causes such a malignancy have poor outcomes. The mortality of HIV patients that have symptomatic effusions is low. If the patient is in cardiac tamponade, this has to be relieved or it could be fatal.
There are many causes of a possible pericardial effusion.
Small pericardial effusions are usually not asymptomatic and have been found in some autopsy studies to have a prevalence of 3%. There are some subsets of patients who have an increased risk of pericardial effusion. These include those with lung cancer. Up to 21% of these patients may have an effusion. Patients with the human immunodeficiency virus have a higher incidence of effusions as well and it has been noted in up to 13%  .
The clinical manifestations of pericardial effusion are dependent on the rate of fluid accumulation. A rapid increase of a small amount of fluid may cause significant symptoms, but the pericardium may accomodate up to 2l slowly over time. The various causes listed above cause the pericardium to secrete more fluid by various methods, either by increased production or decreased absorption .
The pericardium has several functions:
Pericardial effusions, abnormal accumulations of fluid in the pericardial space, may develop slowly or quickly. The normal pericardium can stretch slowly over time to accommodate a gradual increase in the fluid, but it has its limits and the accumulating fluid will exert its pressure on the heart and compromise its function (cardiac tamponade).
It may be sub-classified into: