BACKGROUND: Transcranial Doppler sonography (TCD) of the middle cerebral arteries in patients with prosthetic heart valves reveals high-intensity transient signals (HITS) and can detect asymptomatic cerebrovascular microemboli. Both the nature of the underlying embolic material (either gaseous or corpuscular) and its clinical significance remain uncertain. METHODS: Seventy-one patients undergoing heart valve replacement (n = 63) or repair (n = 8) from June 1996 to June 1998 were prospectively evaluated preoperatively and one week, 3 months and 12 months after valve replacement using TCD. At each follow-up interval, clinical assessment was aimed at detecting neurological events. Furthermore, continuous echo-Doppler study of the carotid arteries and TCD of the middle cerebral arteries for a 30-minute period during each following visit was carried out. RESULTS: No HITS were recorded preoperatively in any patient. At one week, HITS were detected in 25 patients (35%): 22 (65%) of these had received a mechanical prosthesis and three (10%) a bioprosthesis. No HITS were recorded in patients with mitral repair. HITS were subsequently detected only in patients with mechanical prosthesis with a positive TCD at one week, the mean number of HITS per patient being 7 +/- 18 at 3 months and 8 +/- 24 at 12 months. No neurological symptoms were evident in any patients during the postoperative evaluation. Multivariate analysis showed mechanical prosthetic valve to be the only independent predictive risk factor for HITS development. CONCLUSIONS: The role of a mechanical prosthetic valve as a risk factor in the pathogenesis of HITS appears evident. However, HITS appear to be unrelated to possible postoperative neurological events. TCD could have more specific clinical applications if associated with methods that would make it possible to ascertain the nature of various embolic materials.