As indicated in ancient Chinese medical books, Corydalis yanhusuo has therapeutic effects on cardiovascular diseases. The analgesic effect of this plant has been fully elucidated, and l-tetrahydropalmatine has been shown to be the main active principle. The aim of this investigation was to evaluate its protective effects in a rat heart failure model. Rats were subjected to coronary artery ligation, and orally administered with ethanolic extract of Corydalis yanhusuo 50, 100, or 200 mg kg(-1) daily, from the 7th day after surgery. We measured cardiac function, plasma atrial natriuretic peptide (ANP), relative heart and lung weights, infarct size and ventricular dilatation after treatment for 8 weeks. Administration with Corydalis yanhusuo led to a significant reduction in infarct size and improvement in cardiac function as demonstrated by lower left ventricular end diastolic pressure (LVEDP) and elevated +/-dp/dt(max). We also found that Corydalis yanhusuo significantly reduced left ventricular (LV)/body weight ratio, lung/body weight ratio and significantly inhibited neurohormonal activation. Taken together, this study indicated that Corydalis yanhusuo exerted salutary effects on heart failure induced by myocardial infarction in rats.