Matrine, a monomer of traditional Chinese medicine Sophora flavescens, is a potential drug for treatment of arrhythmia. The aim of the study is to elucidate the protective effects of matrine on arrhythmic rat induced by myocardial infarction (MI) and further explore underlying targets. Experiments were performed to investigate the effects of long-term oral administration of matrine on coronary ligation induced arrhythmia, measured in whole animals, via surface electrocardiogram (ECG). Whole-cell patch-clamp technique was used to record the action potential and potassium ionic currents in myocytes isolated from rat hearts. The cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) was measured using the scanning confocal microscopy. Mortality rate was 19/30 (63%) in MI group and 10/30 (33%) in matrine group (p<0.05). This represented a 1.9-fold reduction in long-term mortality rate. The prolonged action potential duration (APD) induced by MI were significantly shortened by long-term treatment of matrine. Matrine restored Kv4.2/I(to), Kir2.1/I(K1) in rat ventricular myocytes after MI. Abnormaly decreased [Ca(2+)](i) mediated by ischemia can be recovered by matrine. Our results suggested that long-term oral administration of matrine reduced arrhythmia and mortality. Electrophysiological experiment revealed that long-term matrine treatment played an important role in anti-arrhythmia through ionic mechanism. Knowledge of matrine from this work may provide insight into the development of new drugs for long-term myocardial infarction treatment.