Hi doctor, whenever I do cardio exercises, I get a bad cough and spit out very dark mucus, and sometimes theres a tiny bit of blood too (just a pinch, and it happens only once). This lasts for about 15-20 minutes after the workout. The deeper the cough, the more black mucus comes out. I also sometimes feel a sharp, pinching pain in the middle of my chest. This has been going on for the past three months. Ive been smoking 4-5 cigarettes a day for the last 7 years. I recently had a medical checkup, and my ECG and chest X-ray were normal. What could be causing this?

It sounds like your symptoms could be related to irritation in your airways from smoking, which may cause inflammation and coughing with mucus. While your ECG and X-ray are normal, I strongly recommend seeing a doctor for further evaluation, possibly including lung function tests, to rule out any underlying conditions like bronchitis or early-stage COPD. Cutting back or quitting smoking will be crucial for your health.