Catalyzes the reversible phosphatidyl group transfer from one phosphatidylglycerol molecule to another to form cardiolipin (CL) (diphosphatidylglycerol) and glycerol (By similarity). May have a role in the heat shock response since the level of the transcript of ywiE increases after a heat shock. 2 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol) = a cardiolipin + glycerol By heat shock. Belongs to the phospholipase D family. Cardiolipin synthase subfamily.