The Collaborative International Dictionary of English v.0.48:

Vitals \Vi"tals\, n. pl.
   1. Organs that are necessary for life; more especially, the
      heart, lungs, and brain.
      [1913 Webster]

   2. Fig.: The part essential to the life or health of
      anything; as, the vitals of a state. "The vitals of the
      public body." --Glanvill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vitals
    n 1: a bodily organ that is essential for life [syn: vital
         organ, vitals]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "vitals":
   abdomen, anus, appendix, blind gut, bosom, bowels, brain, breast,
   cecum, center, center of life, colon, core, deepest recesses,
   duodenum, endocardium, entrails, esoteric reality, foregut,
   giblets, gizzard, guts, heart, heart of hearts, hindgut,
   inmost heart, inmost soul, innards, inner, inner landscape,
   inner life, inner man, inner mechanism, inner nature, inner recess,
   inner self, inside, insides, interior, interior man, intern,
   internal, internals, intestine, intrados, inward, inwards, jejunum,
   kidney, kishkes, large intestine, liver, liver and lights, lung,
   midgut, nerve center, penetralia, perineum, pump, pylorus, quick,
   recesses, rectum, secret heart, secret place, secret places,
   small intestine, soul, spirit, spleen, stomach, ticker, tripes,
   true being, true inwardness, vermiform appendix, viscera,
   vital center, vital principle, works