you might want to go to you er and get checked out this is definatly heart related as i have heard about hsi before
I wouldn't normally try to answer a question like this, as it is impossible to diagnose someone, especially with so little information. However, your description of feeling pressure on your chest and the difficulty breathing - it would seem to be related to your lungs - lung infiltrates often feel like that. Pneumonia for instance. However, it could also be that an injury to your ribs or muscles has made it difficult to breath because of the pain.
How long has this been going on? Do you have a cough? If so, is it productive? (bring up mucous) Have you had any respiratory problems in the recent past? A cold? Fever? Have you had any injury to that area?
I don't want to give any information that would mislead you, but would like to help, as I do know a lot about pulmonary conditions.
Blessings, Jan