Material and Methods: We intended to include 150 patients with an implanted mechanical heart valve (ATS Medical, Medtronic-Hall or St. Jude Medical) in the aortic position between 3 months and 4 years before the analysis. For logistical reasons, the actual number of the patients included was 84. The total conducted valve sound was measured (by a method designed by the authors) for each patient. The measures took place in a bioacoustical laboratory built with a sound-insulated chamber with a very low background noise, designed for the purposes of the study. The measures were performed in German patients followed by "The Heart Centre" in Bad Oeynhausen (Herz- und Diabeteszentrum Nordrhein Westfalen, University of Bochum), where the mentioned laboratory is constructed. The sound analysis of the present study was conducted in a specially designed soundproof bioacoustic laboratory, which isolates the outside sound and vibration from the environment indoors. Inside the laboratory, heavy soundinsulated curtains were placed between the patient and the investigator chambers. The total background noise inside the patient chamber was 19 dB(A), and this was reduced further to 9 dB(A) by using a 250 Hz high-pass filter. The sounds were recorded with the patient in the supine position, and without clothes covering the chest. The valve closing sounds were recorded using a microphone (Brüel and Kjær 4179) placed 5 cm above the patient's chest. This sound was then preamplified (Brüel and Kjær 2660), amplified (Brüel and Kjær 2610) and 250 Hz high-pass filtered (Krohn-Hite 3944) (see Fig. 1). All valve sounds were recorded by the same experienced investigator and stored on an instrumentation recorder (TEAC 510) for later off-line analysis. The data acquisition time for each patient was approximately 10 min.