The critical value of baroreflex sensitivity (BRS) was assessed by spectral analysis of spontaneous fluctuations in pulse intervals and blood pressure. Blood pressure was recorded noninvasively (3 min, controlled breathing 0.33 Hz) in 112 patients, 8-18 days after myocardial infarction (MI). Nine patients died during the first year after MI. BRS was determined as the gain between the spectrum of the variability of systolic blood pressure and the cross-spectrum between the variability of pulse intervals and systolic blood pressure at the frequency of 0.1 Hz. Sensitivity, specificity, and the positive predictive value were calculated in the range of 1-10 ms/mmHg in steps of 1 ms/mmHg. The value of BRS above which sensitivity no longer increases and specificity decreases was taken as the optimal value. The optimal critical value was 3 ms/mmHg.