The effects of levobunolol hydrochlorid (Bun) on the type L calciumchannel currents (Ica) and delayed rectifier potassium channel currents (Ik) in isolated ventricular myocytes of guinea pig were studied by using patch clamp wholecell recording techniques. The results were showed that: 1) Bun caused a dosedependent decrease in Ica and a dose-dependent increase in Ik of the ventricular myocytes.The threshold concentrations of Bun for Ica and Ik were 10-8 mol/L and10-7 mol/L respectively. The maximum effective concentration of Bun for both Ica and Ik was 3 × 10-5 mol/L, and half-maximal concentration was 3 × 10-6 mol/L;2 ) Ik was blocked by 2× 10-6mol/L tetraethylammonium (TEA). A concentration of 3 × 10-6 mol/L Bun showed a decreasing effect on the Ica as revealed by the current-voltage relationship curve, i. e., Bun caused an elevation of the curve; 3)When Ica was blocked by 2 × 10-6 mol/L Isoptin (Verapamil), at a concentrationof 3 × 106- mol/L Bun showed an increasing effect on Ik and the effect could be blocked by TEA. The above-mentioned results indicated that Bun had an inhibito-ry effect on Ica and a fascilitatory effect on Ik The results suggested that themolecular mechanisms of antihypertensive, heart rate slowing and β-receptorblocking effects of Bun might be due to decrease of Ica and increase of Ik. The effects of levobunolol hydrochlorid (Bun) on the type L calcium channel currents (Ica) and delayed rectifier potassium channel currents (Ik) in isolated ventricular myocytes of guinea pig were studied by using patch clamp whole cell recording techniques. The results were showed that: 1 Bun caused a dose dependent decrease in Ica and a dose-dependent increase in Ik of the ventricular myocytes. The maximum concentrations of Bun for Ica and Ik were 10-8 mol / L and 10-7 mol / L respectively. The maximum effective concentration of Bun for both Ica and Ik was 3 × 10-5 mol / L, and half-maximal concentration was 3 × 10-6 mol / L; 2) Ik was blocked by 2 × 10-6 mol / L tetraethylammonium (TEA) concentration of 3 × 10-6 mol / L Bun showed a decreasing effect on the Ica as revealed by the current-voltage relationship curve, ie, Bun caused an elevation of the curve; 3) When Ica was blocked by 2 × 10-6 mol / L Isoptin (Verapamil), at a concentration of 3 × 10 -6 mol / L Bun showed an increasing effector ct on Ik and the effect could be blocked by TEA. The above-mentioned results indicate that Bun had an inhibito-ry effect on Ica and a fascilitatory effect on Ik The results suggesting that themolecular mechanisms of antihypertensive, heart rate slowing and β-receptor block effects of Bun might be due to decrease of Ica and increase of Ik.