1999 Study Showing Placebo Pacemaker Improved Life for Heart Patients and Actually Improved Heart Function.

This is a classic study on placebo effect.  Pacemakers were implanted in 80 people, but only 40 of them were turned on.  Perceptions of improvements by both groups were similar.  While the actual improvements in heart function were much greater in the people with functioning pacemakers, those with pacemakers turned off also experienced significant improvement in heart function.

It appears that perceiving and emotionally feeling that your heart is working better can actually lead to actual improvements in functioning.

http://www.ncbi.nlm.nih.gov/pubmed/10190407