Left ventricular diastolic function was assessed in 17 patients (2 males and 15 females; mean age 44 +/- 9 years) with mixed connective tissue disease (MCTD) and 18 sex- and age-matched healthy control subjects (2 males and 16 females; mean age 44 +/- 8 years) by means of M-mode and pulsed Doppler echocardiography. None had clinical evidence of overt myocardial disease or abnormal left ventricular systolic function. Compared with the control group, patients with MCTD had a significantly longer isovolumic relaxation time (IVRT) (59 +/- 7 versus 70 +/- 12 ms; p less than 0.01), a lower peak early diastolic flow velocity (E) (0.79 +/- 0.10 versus 0.70 +/- 0.07 m/s; p less than 0.005), a higher peak late diastolic flow velocity due to atrial contraction (A) (0.47 +/- 0.08 versus 0.54 +/- 0.08 m/s; p less than 0.05) and a reduced E/A ratio (1.72 +/- 0.37 versus 1.33 +/- 0.26; p less than 0.005). Although there was no significant correlation of left ventricular diastolic filling indexes with age, heart rate, left ventricular end-diastolic and end-systolic dimensions, interventricular septal and left ventricular posterior wall thickness, and fractional shortening, the duration of illness was significantly related to IVRT (r = 0.62; p less than 0.01), peak A (r = 0.79; p less than 0.001) and velocity half-time (r = 0.54; p less than 0.05). The results suggest the presence of an abnormal left ventricular diastolic filling pattern in patients with MCTD and may represent myocardial involvement in this disease.