In 44 patients affected by systemic lupus erythematosus (SLE) without any clinical signs of heart disease (group I) the myocardial performance index (MPI) was calculated to investigate left ventricular function. The index, as the sum of isovolumetric contraction time (ICT) and isovolumetric relaxation time (IRT) divided by ejection time (ET), was measured by tissue Doppler echocardiography (TDE). Results achieved show a prolonged MPI with respect to the values recorded in healthy controls (group II). Its prolongation is due to a significant increase of IRT, whereas ICT and ET were within the normal limits. In patients with SLE without an evident cardiac engagement, this outcome seems to depend on a prevalent diastolic left ventricular dysfunction, perhaps due to a subclinical myocarditis. TDE is more precise than the conventional Doppler method in evaluating MPI and single time intervals, because their measurements are accomplished in concomitance of left ventricular wall motion rather than the flow movement.