When fed furazolidone, 700 ppm, with their mash, most turkey poults develop dilated cardiomyopathy characterized by gross left ventricular dilatation with thinning of both the left ventricular free wall and ventricular septum. Birds fed propranolol, but not digoxin, did not develop this cardiomyopathy. It is not known what pharmacologic property of propranolol conferred protection or if mammals would receive similar protection.