What can help a pulled chest muscle?

Rest!: The only way for the muscle to heal properly is to give it rest. Any movement of the chest wall irritates even breathing. Obviously you can't stop that but you can avoid heavy lifting and reaching which also use the chest wall muscles. Try some arnica and ibruprofen if it is very sore. It can take up to 6 weeks to resolve.

Rest & ...: If you are sure it's a pulled chest muscle, over the counter anti-inflammatory medications (like ibuprofen), warmth, and stretching can help. Massage is helpful as well. If it doesn't get better in 3 days with this you should call your doctor. Also, if the pain is associated with fever, shortness of breath, weakness, or palpitations, you should seek care sooner.