We studied 32 cases of isolated intra-ventricular communication (IVC) in necropsy samples, and made correlations between the size of the failure and the data got from the haemodynamic study, specially the QP/QS, the sistolic pressure of pulmonary arteries (SPPA) and the vascular-pulmonar resistance (VPR). We found no correlation between the size of the orifice and the degree of short-circuit, and the last was no dependant on the SPPA. The SPPA figures were found to be in direct proportion with the failure's area. We found that the short circuit degree is managed by the VPR in inverse relation. We discuss here all the factors involved in the haemodynamic conduct to which we made reference in this paper.