Contribution of transesophageal echocardiography to patient diagnosis and treatment: a prospective analysis. The capability of transesophageal (TEE) versus transthoracic (TTE) echocardiography as a diagnostic tool in clinical practice was prospectively examined in 86 consecutive cases. A conclusive diagnosis was possible in 95% with TEE, whereas the same result was achieved in 48% by TTE. Specifically, TEE provided a conclusive diagnosis in 14 of 16 cases of infective endocarditis, while TTE gave this result in 4 of the 16 cases (p less than 0.001). Similarly, TEE allowed a conclusive diagnosis in 11 of 11 instances of aortic dissection, while TTE gave this indication in two cases (p less than 0.001). TEE was similarly effective in eight of eight cases of atrial thrombi, whereas TTE gave the diagnosis in three of eight cases (p less than 0.01). In five subjects with intracardiac masses, TEE gave a conclusive diagnosis in all five, whereas TTE was able to diagnose conclusively in one subject (p less than 0.02). In seven patients with mitral regurgitation, TEE gave the conclusive diagnosis in all seven and TTE was able to provide this information in four (p = NS). TEE was able to provide a conclusive diagnosis in four patients with aortic insufficiency, and TTE gave the same information in two of the four (p = NS). In 14 patients with prosthetic valve dysfunction, TEE gave the diagnosis in 12 and TTE gave it in eight patients (p = NS). Both methods gave a conclusive diagnosis in 13 out of 13 cases of mitral stenosis (p = NS). Also, TEE provided a conclusive diagnosis in eight of eight patients with adult congenital heart disease and TTE gave this information in four (p = NS). 