Transthoracic echocardiography was performed in 141 patients with 90 Omnicarbon valves in the aortic and 66 in the mitral position. Additionally, 53 of them were investigated by transesophageal echocardiography comparing monoplane and multiplane facilities. The opening direction of the disc and the location of the pivot axis could be correctly determined by transthoracic, monoplane, and multiplane transesophageal echocardiography, respectively, in 100%, 80%, and 100% of the mitral and in 53%, 21%, and 82% of the aortic prostheses. Small regurgitation jets were detected in 90% of the aortic valves (1.6 +/- 0.4 cm2) by transthoracic and in all mitral prostheses (2.3 +/- 0.8 cm2) by transesophageal echocardiography. Based on morphological identification of the pivot points structures, origins of leakage jets were clearly identified as "design-related" in 12% (transthoracic echocardiography of aortic valves) to 100% (multiplane transesophageal echocardiography of mitral valves). In the aortic position, values obtained for transprosthetic forward flow velocity measurements exhibited wide scatter which did not allow a firm separation between valve sizes. No better differentiation was possible by using the calculated Doppler gradients or the velocity time integrals, either. Mean gradients and velocity time integrals showed even smaller differences between groups in the mitral valve patients. It is concluded that the Omnicarbon valve has a suitable design for morphological echocardiographic examination, and multiplane transesophageal technique expands the diagnostic capability. Forward flow measurements do not appear to be suited for detecting a beginning obstruction of this mechanical prosthesis.