The symptoms you are describing sounds like a TENOSYNOVITIS which is an inflammation of the sheaths surrounding the tendon.
It could be due to injury, strain or overuse, an infection, or can be due to unknown reasons.
Just as what you are doing, brace or splint used to immobilize the limb, rest, and anti-inflammatory as Advil are the main treatments. Warm compression application may as well be helphul in relieving pain and inflammation. After recovery, strengthening exercises will help to full recovery and avoid future injuries. In extreme cases, surgery may be required.
If difficulty of staightening the joint or extremity is noted or there are signs of infection, you need to see your doctor for appropriate management and treatment.
Just in case there is any numbness or tingling sensation, the possibility of nerve compression or herniated disc can be given consideration.
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The extent of the symptoms of your condition seems to UNLIKELY related to carpal tunnel syndrome but there is a possibility. There is a simple test that you can do to check on that. At the front side of your left wrist where the median nerve is located, gently tap that area, pain will be intensified if there is a carpal tunnel syndrome.
Other possibilities that had caused your symptoms is a pinched nerve in your neck, shoulder or forearm, diabetic neuropathy or an arthritis at the thumb base. There are more other possibilities and an MRI can help to find out the cause.
With the symptoms you have, association with the heart seems to be the least possibility.