['Progression of heart failure after initial myocardial injury is mediated in part by various redundant inflammatory mediators, including the widely expressed cyclooxygenase-2 (COX-2). Because COX-2 inhibitors are useful in treating many inflammation-mediated diseases, we asked whether COX-2 inhibition can attenuate heart failure progression.', 'Heart failure was experimentally induced in 100 mice by administration of doxorubicin (4 mg. kg(-1). wk(-1) for 6 weeks). Beginning at day 42, mice were fed daily with either COX-2 inhibitor-containing mice chow (n=50) or plain mice chow (controls; n=50). Left ventricular ejection fraction was evaluated as a measure of heart failure by a novel method of transthoracic echocardiography (with intravascular ultrasound catheters) at baseline and on days 42, 56, and 70. From baseline to study termination, left ventricular ejection fraction in COX-2 inhibitor-treated mice decreased significantly less than in control mice (9% versus 29%, P<0.01). Mortality was significantly lower for COX-2 inhibitor-treated mice than for control mice (18% versus 38%, P<0.01). These results were confirmed in a revalidation study in COX-2 inhibitor-treated mice (n=25) and controls (n=25). That study revealed that the hearts from control mice weighed roughly the same as hearts from COX-2 inhibitor-treated mice but showed more extensive signs of cardiomyopathy (as determined by pathological analysis by an independent, blinded observer) and higher levels of COX-2 proteins (as determined by immunoblotting [6442+/-1635 versus 4300+/-2408 arbitrary units, P<0.022]).'] Does cyclooxygenase-2 inhibitor treatment improve left ventricular function and mortality in a murine model of doxorubicin-induced heart failure?