In anatomy, isthmus refers to a constriction between organs. This is a list of anatomical isthmi:

• "Isthmus" the mesencephalon(midbrain)-rhombencephalon(hindbrain) boundary.
• Isthmus faucium (Throat)
• Isthmus glandularis or Thyroid isthmus 
• Isthmus prostatae (Prostate)
• Isthmus tubae auditivae (Eustachian tube)
• Isthmus tubae uterinae (Fallopian tube)
• Uterine isthmus
• Isthmus urethrae (Urethra)
• Isthmus of the aorta
• Isthmus of the Oviduct
• Isthmus of the Rhombencephalon
• Isthmus of the Corpus Callosum
• Isthmus of the Cingulate Gyrus
• Cavo-tricuspid isthmus of the right atrium of the heart, a body of fibrous tissue in the lower atrium between the inferior vena cava, and the tricuspid valve.