We sought to determine whether disruption of the endothelial anti-coagulant activated protein C (APC) pathway in CREBA133 HF mice promotes endocardial thrombosis in the acute decompensated phase of the disease, and whether alterations in von Willebrand factor (vWF) secretion from HF endocardium reduces thrombus formation as HF stabilizes. Here, APC is linked to hydrops fetalis.