Since there are no valves between the pulmonary capillaries and the left atrium, PCWP is a reflection of the LAP. During diastole, when mitral valve is open, the PCWP reflects LVEDP. LVEDP is an index of left ventricular end-diastolic volume.
Here is a helpful URL to further clarify this entry.
http://medind.nic.in/iad/t02/i4/iadt02i4p298.pdf