There is evidence that simply stroking a cat and listening to the purr
after a hard day has this effect, but did you really need to ask..?! Seems
obvious to me :-)

Ivor

Yes.  It is a proven fact.   So much so that some hospitals have set
up "pet visiting days" where patients can visit with their cats in the
lobby or a room set aside for the purpose.  

Also pets are a great therapy tool for patients in hospitals.

Yup. Has been scientifically observed, but I think people who like petting
cats/dogs etc. can tell you how nice/relaxed it makes them feel them without
taking measurements!  :)

http://www.holistic-online.com/stress/stress_pet-therapy.htm

alex