Parts of the olive tree are used for medical reasons for hundreds of years, for example as an agent against high blood pressure in Italy. Especially the leafs are containing a very high concentration of Oleuropein, the effective substance. Although being sold by many pharmaceutical or nature medicine providers the cellular mechanisms of action remain still unclear. Results of mapping experiments of our working group have shown a prolongation of atrioventricular conduction, negative inotropy, bradycardia and vasodilatation as indications for olea europea extract possibly being an antagonist on calcium channels in mammalian heart. Therefore, we investigated the conductance of L-type calcium channels in cultured neonatal rat cardiomyocytes performing a perforated patch clamp technique using Amphotericin B. We tested a final extract concentration containing 20 mmol Oleuropein. We found that olive leaf extract suppresses the L- type calcium channel directly and reversibly in cultured neonatal rat cardiomyocytes. There was a decrease of 28% in L-type calcium channel maximum current. Our results may help to understand the actions of mechanism of the olea europea extract known in herbal medicine for a long time.