Using whole-cell patch-clamp technique, the effect of radiofrequency catheter ablation (RFCA) on calcium current (Ica) of guinea pig ventricular myocytes was examined. The radiofrequency energy delivered was 20 W x 10 s. RF-CA decreased Ica apparently with the affected area reaching up to 1.2 cm from the ablation focus. In the meanwhile, the pathological lesion size resulted from RFCA was merely 0.41 +/- 0.11 cm. These findings indicate that RFCA, apart from causing tissue necrosis by heat, can affect myocyte membrane currents in a large area. This may explain why RFCA has a very high success rate with a small pathological lesion.