Sarafotoxin-i3 from Atractaspis irregularis is a long sarafotoxin with an extended C terminus extension. Sarafotoxin-b from Atractaspis engaddensis is shorter by four amino acids. These peptides belong to the endothelin-like peptide family with a high sequence homology and similar three-dimensional structure. They act on endothelin receptors situated on the membrane of endothelial and smooth muscle cells. However, SRTX-i 3, despite a high toxicity, has a very low affinity for endothelin receptors compared to SRTX-b. The present work was carried out in order to compare the precise in vivo cardiovascular effect of SRTX-b and SRTX-i3. Male Wistar rats were anesthetized and mechanically ventilated. Doppler echocardiography was performed to measure left and right ventricular functions. The rats were divided into three groups that received intravenous injections of: saline, SRTX-b or SRTX-i3. All measurements were taken at baseline, at 1 min and at 6 min after injection. Both toxins impaired cardiac output. SRTX-b impaired left ventricular function, while SRTX-i3 increased airway pressures and led to acute right ventricular dilatation associated with a decreased tricuspid annulus peak systolic velocity. SRTX-b and SRTX-i3 appear to exert toxic effects via different mechanisms, SRTX-b impairs left ventricular function, while SRTX-i3 increases airway pressures and impairs right ventricular function.