Brief Answer:
Urgent EKG recommended- other causes as explained

Detailed Answer:
Hi,
Thanks for your query, albeit short and specific.

Since there is heavy uncomfortable feeling under left breasts, considering your age, an urgent EKG and cardiac evaluation is a must to rule out or confirm any cardiac-related problems.

Other probable causes can be as follows if cardiac problems are ruled out:
Costochondritis.
Myalgia.
Lump in breast.
Problem with Pleura and/or lung underlying the affected area.

Please get the EKG done in the first place.

Please give additional information for me to assist you better:

Is there local tenderness on pressure?
Does the movement of the chest like coughing increase pain/discomfort?
Any swelling, redness, rash?
Any upper/mid backache?

I hope this answer helps you.
Let me know if I can assist you further.

With Regards.

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