A cylindrical barium titanate element placed at the distal end of a specially designed catheter was used in studies of the heart sounds of dogs and humans. The sounds were recorded on tape and simultaneously on a photographic galvanometer recorder with the element located in the four chambers of the heart and in the great vessels leading from the heart. The location of the catheter tip in each case was followed by X-ray, and the studies were continuously monitored by Ecg. Sound spectrographic analyses of the several sounds were made and analyzed.