It showed that there was insufficient formation of the endocardial cushion. Myocytes initiate rhythmic electrical activity, before the fusion of the endocardial tubes. Tissue masses called endocardial cushions develop into atrioventricular and conotroncal regions. The IV septum grows upward towards the endocardial cushion. EFE can now be found non-invasively by the recording of increased endocardial echos. During ventricular contraction, the wave of depolarization moves from the endocardial to the epicardial surface. Endocardial cells begin to form the myocardium. However, the yolk sac, extra-embryonic membranes, egg membranes and endocardial tube are considered caenogenetic features. BMP signal derived from myocardium is also involved in endocardial differentiation during heart development. The term "endocardial fibroelastosis" was introduced by Weinberg and Himmelfarb in 1943. More specifically, they form from endocardial tubes, starting at day 21. The endocardial cushion serves as a makeshift valve until then. On autopsy, most of these patients' hearts showed the thickened endocardial layer noted above. The septum primum eventually fuses with the endocardial cushion, closing the ostium primum off completely. Endocardial Solutions manufactured diagnostic and therapeutic devices used to treat atrial fibrillation.