However, despite extensively characterized clinical significance of OPN and Grem1 changes in ischemic HF-associated cardiac injury context, most of the studies present correlative analysis of OPN, Grem1 expression changes and clinical parameters of progressing cardiac dysfunction relying on the blood plasma levels of these proteins [6,13,21,22], without documenting the actual primary source of these changes within myocardial tissue. This evidence concerns the gene GREM1 and hydrops fetalis.