There are several factors to analyze when the left side of the rib cage is distended and painful after eating. The first one is a functional pain without any etiology, often the patient eats too much hunger stretches the lungs and then radiates to the right left side of the subcostal pain This case does not require special treatment, only the amount of control in the diet can achieve a significant relief. The second is the presence of gastric ulcers, because gastric ulcers after a full meal pain will be more obvious, radiating to the left side of the rib cage, to confirm the diagnosis of this disease to do gastroscopy will be simple and clear. The third kind of pain under the ribs on the left side after eating is considered to be a possible combination of coronary heart disease, which requires an electrocardiogram or coronary angiography to determine. The last type is pancreatic head cancer or pancreatic cancer or pancreatic cyst, these diseases will also cause pain and distension under the left side of the ribs due to pressure on the pancreatic mass after a full stomach, this requires an abdominal ultrasound, primary screening or an abdominal MRI to clarify.