8-oxyberberine (8-Oxoberberine, JKL1073A), an oxoderivative of berberine, is an alkaloid isolated from Argemone mexicana. 8-oxyberberine has been initially reported to exert anti-proliferative effects against a series of cancers. 8-oxyberberine inhibited the cell proliferation in human colon cancer cells. 8-Oxoberberine, a derivative of berberine, has been reported to exert antiarrhythmic activity, much like a class III antiarrhythmic agent. 8-Oxoberberine, like berberine, exerted positive inotropic and negative chronotropic actions. In rat left atria 8-oxoberberine, 10 to 100 uM, increased atrial contractility. In spontaneously beating right atria, 8-oxoberberine increased atrial contractility but slightly decreased the rate of contractions. 8-Oxoberberine inhibited the integral of the transient outward current (Ito) with a KD value of approximately 4 uM in either human or rat atrial myocytes. 8-Oxoberberine inhibited Ito by binding to open-state channels or by shifting the steady state inactivation curve of Ito.