SUMMARY1. The electrophysiological effects of changrolin (CRL), a Chinese antiarrhythmic drug derived from a traditional anti‐malarial plant, were examined using the whole‐cell patch‐clamp method on single cells isolated from guinea‐pig and rabbit hearts.2. At a clinically relevant concentration of 50μmol/L changrolin inhibited Ica. by 19.3 ± 6.0% and 17.3 ± 2.6% in guinea‐pig and rabbit ventricular cells, respectively. The voltage‐dependent channel availability curve was not affected. The CRL effect was enhanced to a small extent during a repetitive stimulation at 2 Hz.3. Inawas resistant to CRL and the channel availability curve was also unaffected. A small use‐dependent inhibition was observed only when the Inawas elicited at 5 Hz in the presence of 300 μmol/L CRL.4. At 50 μmol/L, CRL did not affect the time‐independent inward rectifier and the delayed rectifier K+currents (Iki and Ik, respectively), but inhibited the transient outward current (Ito) by 17.7 ± 2.4%. Changrolin significantly shortened the action potential duration in both guinea‐pig and rabbit ventricular cells.5. In conclusion, CRL inhibits Icaand Ito but h