Snake venoms contain a large number of pharmacologically active molecules that cause harmful effects and one of them is phospholipase A2 (PLA2). PLA2 belong to a group of enzymes that hydrolyze the ester bond of phospholipids. In nose-horned vipers (Vipera ammodytes), the most venomous European snakes, three toxic phospholipases called ammodytoxins have been found. Ammodytoxins are isoenzymes which can be found in isoforms A, B and C. Primary structures of all three isoenzymes are very similar, but the proteins differ in toxicity. The most toxic isoform is ammodytxin A (AtxA). AtxA is homodimer consisting of 122 aminoacid residues. The cofactor \(Ca^{2+}\) is required for formation of enzyme-substrate complex. Besides its enzymatic role, AtxA has mechanisms for presynaptic neurotoxicity. Presynaptic neurotoxicity is achieved by binding to a specific intracellular and membrane proteins such as R180, R25, calmodulin (CaM), human coagulation factor X (hFXa) and many others. Even though exact enzymatic molecular mechanism is not completely resolved it is assumed that it goes through three phases. Ultimate neurotoxic effects lead to an irreversibile blockade of acetylcholine release. The most important aminoacid residues involved in presynaptic neurotoxicity are located in β-helix, C-terminal (YIRN region, Phe124) and N-terminal region (Phe24). Besides causing neurotoxic effects, nosehorned viper venom also causes various chemotoxic and cytotoxic symptoms. The most potent antivenoms have polyvalent properties and can neutralize harmful effects of several venomous snakes.