Is left sided chest pain always due to heart disease?

Heart disease is only one cause of chest pain. Diseases of other organs of the chest can also cause chest pain. Pain can originate from the skin, muscles, bone, lung, covering of the lung (pleura) and food pipe (esophagus). Inflammation of the pleura is known as pleurisy. Nature of the pain and associations often help in differentiating the origin. For example, pain arising from the skin will often be associated with redness and local tenderness. Pain arising from the lung or pleura can increase on deep breathing and coughing. Muscle pain is aggravated by movement of the involved muscle. Bone pain also can be increased by local movement and associated with local tenderness (pain on local pressure with the hand).

Pain may arise in the nerves (nerve root pain) of the chest wall. For example, in a condition called Herpes Zoster, chicken pox virus involves the sensory nerve roots, producing severe pain localised to the region of the skin supplied by the concerned nerve. Pain starts a few days prior to the eruptions in skin so that it may be mistaken for other causes of chest pain in the initial days. Diagnosis is clear when the vesicles appear on the skin in the distribution of the nerve supply, strictly to one side of the midline of the body. In this condition the pain may sometimes persist long after the healing of the vesicles (post herpetic neuralgia). Pain can also be due to damage or compression of the nerve root by bony structures or masses within the spine from where the nerves arise.

Thus a lot more illnesses than heart disease can cause chest pain, either on the left or right side and it needs careful evaluation and work up to identify the exact cause.