Aim of this study is to define the hemodynamic effects of magnesium (Mg) in patients with ischemic heart disease. Thus, the effects of 1 g of Mg pidolate injected over 3 min iv were evaluated in 10 patients by analysis of pressure data from a micromanometer catheter in the left ventricle and of volume data derived from Doppler and 2-dimensional echocardiography. Recordings were made before and immediately after the injection, at 3, 5, and 8 min. At 5 min, Mg induced a significant reduction in left ventricular peak systolic pressure (from 132.4 +/- 19.4 to 122.7 +/- 17.5 mmHg, p = 0.015, with early filling notably augmented (E wave of Doppler curve; from 39.4 +/- 8.5 to 43.9 +/- 9.7 cm/s, p = 0.013) and a slight increase in cardiac output (from 6.23 +/- 1.4 to 6.9 +/- 1.7 l/min, p = 0.092). Heart rate increased (from 75.9 +/- 9.6 to 78.13 +/- 8.4 b/min, p = 0.062) and the constant of isovolumetric pressure decay decreased (from 48.9 +/- 13.2 to 45.7 +/- 14.9 ms, p = 0.065), probably as a final effect of aortic pressure reduction. The diastolic pressure-volume relationship was insignificantly displaced downward (p = 0.11) and to the right (p = 0.62). In conclusion, Mg unloads the ischemic left ventricle through a reduction of systemic aortic pressure, with a secondary increase in early filling; this increase may derive from a rise in the atrioventricular diastolic gradient, subsequent to an improvement in ventricular emptying. Active relaxation is improved, and passive diastolic properties are not affected, in spite of the reported calcium-antagonist action of the drug.