Arterial hypertension is a cardiovascular disease prevalent in black African countries. Its prevalence is 5 to 20% in sub-Sahara African countries and 20% in Côte d'Ivoire. Despite the variety of antihypertensive drugs available in modern medicine, the disease persists. Hence the search for natural products with potential anti-hypertensive properties is ongoing. This study focused on the effects of aqueous leaf extract of Lophira lanceolata on the arterial blood pressure (BP) and electrocardiography (ECG) in rabbits. Phytochemical analysis was carried out in order to determine the phytoconstituents contained in the extract. Varied L. lanceolata macerate doses (0.5 to 50 mg/kg bw) were administered to anesthetized rabbits intravenously. The carotid artery was intubated using a catheter connected to Ludwig's mercury manometer for BP measurement. The recording of the ECG was performed using an electrocardiograph. The phytochemical screening revealed the presence of phytoconstituents including polyphenols, flavonoids and alkaloids in L. lanceolata. The results showed that L. lanceolata induced a dose-dependent hypotension with a fifty percent effective dose (ED50) equal to 5.36 mg/kg bw. in normotensive rabbits. The hypotension induced by the extract was significantly (p<0.01) reduced up to 60% by atropine, an acetylcholine muscarinic receptor antagonist. In addition, the extract significantly (p<0.001) decreased the hypertension induced in rabbits with adrenaline up to 70%. On the ECG, the extract caused significant decreases (p<0.001) of the amplitudes of the P waves, T waves, the QRS complex and the PQ and QT intervals. However, the heart rate increased significantly (p<0.001). The usefulness of L. lanceolata in traditional medicine for the treatment of hypertension is potentiated. It is therefore important to encourage its use.