I'm a 56 yo female recently had chest pains under my left breast. Only had it once so far while I was walking up a hill.

A concern. Exertional chest pain is always a concern. You should see your doctor promptly, even if it's not recurring. A stress test if often very useful to distinguish heart symptoms from other causes like muscular strain or acid reflux.

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I'm having a dull chest pain on my left breast bone and it feels sharp when walking I don't know what it could be can you give an answer?

Pain. you may have strained or pulled a muscle in your chest,called an intercostal muscle. Try some moist heat applied to the chest wall and Aleeve 200 mg, two tabs once a day with food. Read more...