Although Lycopus lucidus Turcz has long been used in the Oriental traditional medicine, effects of Lycopus lucidus on the cardiac function have not well been documented. The purpose of the present study was to test the effects of ethanol extract of Lycopus lucidus Turcz (ELT) on atrial dynamics in beating rabbit atria. ELT increased atrial dynamics including stroke volume and pulse pressure in a concentration‐dependent manner without changes in cAMP efflux. ELT‐induced positive inotropic effect was blocked by diltiazem, an inhibitor of L‐type Ca2+ channel. Blockade of the Ca2+ release from the sarcoplasmic reticulum by combined treatment with ryanodine, a SR Ca2+ release‐selective inhibitor, and thapsigargin, a SR Ca2+ ATPase‐selective inhibitor, significantly attenuated ELT‐induced inotropic effect. In addition, betulinic aicd (BA), a well known pentacyclic triterpenes constituent of ELT, also increased atrial stroke volume and pulse pressure without alteration of the cAMP efflux level.Increases in atrial dynamics by BA were blocked by pre‐treatment with diltiazem, but was not altered by pre‐treatment with staurosporine. These results suggest that the ELT‐induced positive inotropic effect in beating rabbit atria may, at least in part, be due to the activity of L‐type Ca2+ channels and be related with BA.