Middle back pain: Back pain in the middle back area. See detailed information below for a list of 31 causes of Middle back pain, Symptom Checker, Assessment Questionnaire, including diseases and drug side effect causes. Â» Review Causes of Middle back pain: Causes | Symptom Checker Â» | Assessment Questionnaire Â» Causes of Middle back pain:
Valvular Heart Disease. Disorders of certain heart valves can also lead to left atrial enlargement. The mitral valve separates the left atrium from the left ventricle. If the mitral valve becomes narrow -- a condition known as mitral stenosis -- blood accumulates in the left atrium and causes enlargement.
Possible causes of mitral valve regurgitation include: 1  Mitral valve prolapse. 2  In this condition, the leaflets and tendon-like cords supporting the mitral valve weaken and stretch so that with each contraction of the left ventricle, the valve leaflets bulge (prolapse) into the left atrium.