If you have aggrevated your chestmuscles with improper progression of chest flies, then ice it for atleast 3 days. If it is costocondritis, it had to be a really heavy workout.
Also look at the possibility of taking an intiinflammatory if there is constant pain at rest.
Stretching of pectoral muscle with arm below the shouder, at shoulder level and above shoulder level at a door way. Start holding for 10 secs then after 3 days progress to 20 or 30 seconds. * Never stretch into pain.
** If tightness is like a heart burn or tightening around chest, which comes and goes, check with your GP for cardiac related issues immediately. If any shortness of breath or fever get it checked immediately....
If a postural problem please make use of an online consultation.
Next Steps
Icing as per prescription above.
Tightness could also be important indication of a cardiac issue, so please take an online GP consultation with Practo.
Health Tips
stop exercising with the arms till symptoms abate.