Every time i sit or stand a certain way i get numness in my left arm. right now i don't feel it, ?

? heart problems: The brachial plexus controls the nerves that go to your arm. However, positional changes bring up issue of poor blood flow. Some patients with heart problems will get pain and numbness down the left arm. Subclavian steal syndrome can cause similar symptoms. A thorough medical evaluation would be appropriate with attention to the heart and structures in the upper chest.