  In external galaxies, some galaxies have higher activities of star formation
and central supermassive black holes. The interstellar medium in those galaxies
can be heated by different mechanisms such as UV-heating, X-ray heating,
cosmic-ray heating, and shock/mechanical heating. Chemical compositions can
also be affected by those heating mechanisms. Observations of many molecular
species in those nearby galaxies are now possible with the high sensitivity of
Atacama Large Millimeter/sub-millimeter Array (ALMA). Here I cover different
chemical models for those heating mechanisms. In addition, I present recent
ALMA results of extragalactic astrochemistry including our results of a face-on
galaxy M83 and an infrared-luminous merger NGC 3256.
