Hi, do you think it's a heart attack or something else?

I dont know what the "heart testing machine". Did you mean they took an ECG? (Electrocardiogram, by placing the electrodes on left side of your chest, wrists, and on your feet? ECG cannot always detect a heart problem at a resting stage. You must see another doctor and get through a TMT (Tread mill test) which will determine if you have any ischaemic heart issues - lack of blood supply to your heart. Some of the symptoms you mentions like pain in the stomach area (this should be just below the sternum, central bone of your rib cage running from below your chin to stomach area), and pain on the shoulder etc. Do not rely on just one simple test, and go for further checks before you rule out. A good cardiologist should rule out heart problems, and then you may have to see another doc to see if you have any acidity related problems. Sometimes even gas build up in the stomach can cause severe pain on the left side of the stomach below or around the left part of the rib cage...