EDN1 and hydrops fetalis: The imbalance of mitogenic (endothelin-1, interleukin-1, vascular endothelial growth factor, etc.)and vasoactive (endothelin-1, thromboxane A, serotonin, etc.)mediators result in a predominantly vasoconstrictive atmosphere and can result in structural remodeling of the vascular endothelium and underlying smooth muscle.3 Interestingly however, the degree of PH in HF is highly variable for a given degree of left ventricular dysfunction and disease severity, suggesting the possibility that genetic variation may influence the susceptibility to PH in HF.