The heart is surrounded by a double-layered, sac-like structure called the pericardium. The space between the layers normally contains a very small amount of fluid. When the volume of fluid exceeds the pericardium's "full" level, pericardial effusion puts pressure on the heart, causing poor heart function. Chronic pericarditis may cause the pericardium to lose its elasticity, causing a constriction of the heart.
To answer any questions you may have depends on the severity, chronic or acute, symptoms if any, etc. If the condition is advanced there may be chest pain, shortness of breath, fatigue, any activities that cause symptoms should be avoided.