Objective To investigate the effects of angiontensin II receptor antipeptide (AngII antipeptide) on I K(ATP) , I Ca L , I K and I ti of guinea pig ventricular myocytes. Method Whole cell patch clamp technique was used. Results (1) I Ca L was inhibited by AngII antipeptide (5 μmol/L) (from -0 75±0 16 to -0 42± 0 09 nA, n =10, P< 0 05), but the shape of I V curve was not changed. (2) I K(ATP) was inhibited by AngII antipeptide (5 μmol/L) (1 52±0 24 to 0 94±0 13 nA, n =10, P < 0 05). (3) Both I K and I K·tail were inhibited by AngII antipeptide (5 μmol/L) (0 96±0 10 and 0 45± 0 08 nA to 0 40±0 06 and 0 18±0 06 nA, n = 8, P< 0 05, respectively). (4) In low K + high Ca 2+ solution, I ti was inhibited by AngII antipeptide (5 μmol/L) (-0 41±0 11 to -0 19±0 06 nA, n = 9, P< 0 05), and I ti lag time was significantly prolonged from 165±23 to 204±25 ms ( n = 9, P< 0 05). (5) AngII antipeptide (5 μmol/L) had no effects on I K1 . Conclusion AngII antipeptide might protect the ischemic cardiomyocytes and prevent arrhythmia.