This study determined plasma glucose, free fatty acid(ffa), epinephrine, norepinephrine, creatine the phosphokinase(CPK), calcium (Ca), magnesium(Mg) and hydroxyproline, Ca and Mg in the heart muscle. Thirty six male Sprague Dawley rats average weighing 110g divided into two diet group : normal Mg group(0.05% Mg), Marginal Mg group(0.005% Mg). After the rats were on experimental diets for 2 weeks, rats for each group were randomly assigned to stress and no stress group and 30 minutes IMMB stress was administered to stress group every day for two weeks. The following were found : 1) Rats fed normal magnesium diet showed decreased plasma glucose and non signficant change in norepinephrine and CPK with IMMB stress, while magnesium deficient rats showed elevated plasma glucose, norepinephrine and CPK with stress. 2) Myocardial hydroxyproline and plasma epinephrine were not significantly different among groups. 3) In the rats fed adequate magnesium, stress increased plasma magnesium while rats on marginal magnesium diet did not show significant change with stress. 4) Plasma and myocardial calcium were increased in rats fed marginal Mg diet, but did not show any significant difference with stress.