What's the difference between pericarditis and pleurisy?

Area of inflammation: Pericarditis refers to inflammation of the pericardium, the lining around the heart. Pleurisy refers to inflammation of the pleura, the lining of the lungs. Many possible causes, but viral infxns are most common. There's some overlap, where the lungs border the heart & both cause sharp chest pain, but pleurisy is more obviously breathing-related while pericardial pain is affected by position.

Different organs: The pericardium is a membrane that surrounds and protects the heart. When it is inflammed, for example by infection, the condition is called 'pericarditis'. The pleura are two membranes that surround and protect the lungs. Inflammation of these structures is called 'pleuritis' or 'pleursy'. The two structures are close to eachother, so symptoms can overlap.