The anatomic structures of the heart and mediastinum can be demonstrated with MRI in three dimensions in their topographic order without contrast medium or heart catheterization. Furthermore, differentiation of the tracheobronchial system and the mediastinal lymph nodes can be discerned with MRI. MRI offers the advantages of reducing invasive diagnostic procedures, eliminating radiation hazards and avoiding the risks of contrast media. Only in the area of the structures adjacent to the diaphragm an improvement of the images by means of additional respiratory-gating is desirable. Concerning tumors in the mediastinum, MRI supplies essential information for the planning of therapy.