Constant light pain on the left side of the chest for a period not shorter than half and year may have many causes, starting from musculoskeletal disorders to heart-related diseases. Your foster father should also seek professional advice from a cardiologist to query through his heart history and check it out, via tests such as an ECG of X-ray for the identification of its cause. He should get prompt medical attention to rule out any serious conditions and ensure his health.

Since this left sided chest pain has been persistent for 6 months, therefore it could be as a result of following conditions:
1.) Angina: Is a symptom of any heart related problem such as coronary heart disease. It describes chest pain, discomfort, or pressure that you get, when your heart muscle isn’t getting enough oxygen from blood. You might also have discomfort in your arms, shoulders, neck, back, or jaw.

2.) Heart attack: A heart attack takes place when the heart muscle is damaged because it can’t get enough supply of the oxygen-rich blood. Some heart attacks start with mild chest pain that builds up slowly. And in other cases they can also start abruptly, with intense pain on the left side or center of your chest.

3.) Myocarditis: Chest pain can also be a sign of heart inflammation. Myocarditis can affect your heart’s electrical system, weakening your heart or causing permanent damage to the heart muscle.

4.) Cardiomyopathy: Cardiomyopathy is a disease of heart muscle or enlarged heart. It’s possible to have cardiomyopathy without symptoms, but it can certainly cause chest pain.

5.) Pericarditis: Pericardium is the two thin layers of tissue that surround the heart, when it becomes inflamed or irritated, it leads to a sharp stabbing pain on the left side or middle of the chest. You might also have pain in one or both shoulders.

6.) Hiatal hernia: A hiatal hernia is when the upper part of your stomach pushes through the large muscle between your abdomen and chest (diaphragm).

7.) Problems with your esophagus: Chest pain can signal that there’s something wrong with your esophagus.
For an instance, an esophageal muscle spasm can cause the same type of chest pain as a heart attack.

Also, if the lining of your esophagus becomes inflamed, then it can cause burning or sharp chest pain.

Furthermore, an esophageal rupture, or tear, allows food to leak into your chest cavity, causing mild to severe chest pain. It can also lead to nausea, vomiting, and rapid breathing.
8.) Pulled muscles and chest wall injuries: Chest pain can be caused by pulled, strained, or sprained muscles in either the chest or between the ribs. Any injury to your chest can lead to pain.

9.) Collapsed lung: This can be caused by disease or trauma inflicted upon the chest.

10.) Pneumonia: Sharp or stabbing chest pain that worsens on taking a deep breath or while coughing could point at pneumonia, especially if you were recently infected by a respiratory illness such as bronchitis or influenza.

11.) Lung cancer: Chest pain can sometimes be a symptom of lung cancer. Symptoms don't necessarily appear in the earlier stages. The sooner you’re diagnosed and treated however, the better will be outcome.

12.) Pulmonary hypertension: is high blood pressure in the lungs.

13.) Pulmonary embolism: Meaning a blood clot in the lungs.
It would be better if you get your father diagnosed as soon as possible, please refer our page Pulmonologists in Mumbai, if you need some other city covered or ever feel confused then you can always come to us.