Extreme pain left side of chest and numbness in left arm?

Extreme sounds bad: Extreme symptoms means it's extremely important to see a doctor. A person with left chest pain must see the doctor right away to find out why. He should be going to the ER. If it turns out to be a heart problem or heart attack, a collapsed lung, a pneumonia, a blood clot in the lung, bad heartburn, costochondritis (inflammation of the rib joints), etc..., he will be in the right place at the ER.