The effect of magnesium deficiency on postischemic myocardial dysfunction (myocardial stunning) in an open-chest swine model was studied. Twelve swine were assigned either to low magnesium diet or control diet. Myocardial stunning was assessed by measuring regional wall thickening by epicardial Doppler before and after brief occlusion (8 min) of the left anterior descending coronary artery. Serum magnesium levels decreased significantly in the experimental group only. Glutathione levels were 42.6% lower in the magnesium deficient swine than in controls. Stunning time was significantly prolonged from 32.8 +/- 3.1 min in the control group to 43.8 +/- 4.6 min in the hypomagnesemic swine. In conclusion, magnesium deficiency is associated with prolonged recovery from myocardial stunning.