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Twenty-one dogs were chronically instrumented with ultrasonic left ventricular dimension transducers and micromanometers to elucidate the effects of acute protein-calorie malnutrition on cardiac function. Ten dogs received a regular diet for 3 wk, whereas 11 dogs received a protein-calorie-deficient diet designed to achieve a mean weight loss of 20-25% over a 3-wk period. Studies of cardiac function were performed in awake intact animals at base line (1 wk postoperatively) and after 3 wk. In the malnourished dogs, cardiac mass was lost in proportion to total body mass loss. Mean cardiac mass fell from 115 to 91 g. This was largely due to wall thinning in this group. Heart rate dropped from 125 to 79 beats/min with malnutrition and ejection fraction increased from 29.8 to 34.6%. Cardiac output fell from 2.98 to 2.38 l/min, but cardiac index normalized to body surface area was unchanged. No significant changes in hemodynamics were observed in the control group. In the malnutrition group, global ventricular contractility, as measured by the load-independent index of systolic function or the slope of linear relationship between end-systolic pressure and end-systolic volume (EmaxPV), decreased slightly from 3.56 to 2.81 mmHg/ml (P = 0.07). However, Emax calculated from circumferential stress and strain data was unchanged. This indicates that depressed contractility was due to loss of cardiac muscle mass rather than any change in the myocardium per se. Response to beta-adrenergic stimulation was unchanged with starvation. Acute protein-calorie malnutrition causes significant cardiac atrophy that is reflected in decreased cardiac output and slightly reduced contractility but not in intrinsic properties of the myocardium.