Hi! Welcome to HCM and thank you for your question! There are two possibilities (and it is good that your heart is ok) that we can consider - both of which can be due to a bad workout. First, you may be suffering from costochondritis
, an inflammation of the rib or its joint, which causes flares of pain especially when taking deep breaths or during physical activity. The second and more worrisome, is, you may have strained or torn your pectoralis muscle. I am recommending that you see a sports medicine
expert or a physiotherapist so that the appropriate tests can be done to guide your treatment plan. In the meantime, rest and do not exert the affected area. Also, remember that it is important to stretch and observe proper technique during weightlifting/workout sessions to avoid injuries like this. I hope you feel better soon! Take care!