Twenty-one dogs underwent instrumentation of the left ventricle with ultrasonic dimension to study the effects of acute protein-calorie malnutrition on the adrenergic responsiveness of the heart. This study allowed a chronic and dynamic measurement of the major cardiac axes and the ventricular wall thickness, which in turn can be used to derive sophisticated measurements of global and intrinsic left ventricular function. Of the 21 dogs, 11 received a protein- and calorie-deficient diet designed to achieve a mean weight loss from a baseline of 20-25% over a 4-week period. The other 10 dogs received a normal diet. Dogs were also randomized to receive either acute propranolol beta-receptor blockade (n = 9) or acute isoproterenol beta-receptor stimulation (n = 12) during their baseline studies. Of the nine dogs given propranolol, five were subsequently malnourished and four served as controls. of the 12 given isoproterenol, six were rendered malnourished and six were controls. All dogs were studied at both baseline and 4 weeks and received drugs in an identical fashion during both studies. The significant changes with malnutrition consisted of decreases in heart rate, cardiac mass, and left ventricular wall thickness. The degree of change in stroke volume, ejection fraction, cardiac output, dp/dt, and E(max) (index of left ventricular contractility), with the administration of propranolol or isoproterenol was unaltered by malnutrition. These data support the contention that moderate protein-calorie malnutrition is well tolerated in instrumented, unstessed dogs and that the left ventricle's capacity to respond to beta-stimulation and to tolerate beta-blockade is largely unimpaired.