Pain on the left side of the lower ribs may be caused by costochondritis, stomach disorders, and heart disease. 1. Costochondritis: is inflammation of the cartilage that connects the ribs to the sternum. It can be caused by an injury or strain in the area, or by an infection, such as a respiratory infection. It can cause a sharp, stabbing pain that worsens when coughing, sneezing or pressing on the ribs. 2. Stomach disorders: gastric ulcers, for example, can cause severe pain in the middle of the abdomen just below the chest and can be accompanied by indigestion. Gastroenteritis may cause pain below the left rib cage and may be accompanied by fever and diarrhea. 3. Heart disease: such as angina pectoris, myocardial infarction, etc., will lead to pain under the left rib cage, which may be accompanied by chest tightness and shortness of breath. It is recommended that patients seek timely medical attention, under the guidance of the doctor for a detailed examination, to clarify the cause of the disease and then symptomatic treatment.