Left shoulder pain is most often caused by a musculoskeletal problem: an inflamed tendon, a torn rotator cuff, or a strained muscle. But because the left shoulder is also a common site for referred pain from the heart, spleen, and neck, the location matters more than it would for right-sided shoulder pain. Understanding the difference between a local injury and a warning sign from somewhere else in the body is the first step toward figuring out what’s going on.
Rotator Cuff Injuries
The rotator cuff is a group of four tendons that hold your upper arm bone in the shoulder socket and let you lift and rotate your arm. These tendons are the most common source of shoulder pain, and injuries range from mild inflammation to complete tears.
Tendinitis happens when one of these tendons becomes inflamed, usually from repetitive overhead motions like throwing, painting, or swimming. Acute tendinitis comes on after a burst of activity. Chronic tendinitis develops gradually from years of wear and tear or from degenerative conditions like arthritis. The pain typically worsens when you reach overhead or behind your back.
Tears can be partial, where the tendon thins but stays attached to the bone, or full-thickness, where part or all of the tendon detaches completely. A full-thickness complete tear essentially leaves a hole in the tendon. Partial tears often cause a deep ache that gets worse with use, while complete tears can make it impossible to lift your arm away from your body. Tears can happen suddenly from a fall or develop slowly over years of overuse.
The good news: about 75% of patients with rotator cuff tears who follow a structured physical therapy program improve enough to avoid surgery within two years. When surgery is needed, it’s typically outpatient, but recovery requires six to eight weeks in a sling followed by months of physical therapy, with full recovery taking five to six months.
Bursitis and Impingement
Between the rotator cuff and the bony top of your shoulder blade sits a small fluid-filled sac called a bursa. Overuse of the shoulder can inflame this sac, a condition called subacromial bursitis. It often develops alongside rotator cuff tendinitis, and the two can be hard to tell apart because they cause similar pain with overhead movement.
Impingement is the mechanical problem that often drives bursitis and tendinitis. When you lift your arm, the top of your shoulder blade can press down on the rotator cuff tendons and bursa, pinching them with each movement. Over time, this repeated compression causes inflammation, pain, and limited range of motion. Everyday tasks like combing your hair or getting dressed become painful. The hallmark of impingement is pain that starts when your arm is about halfway up and intensifies as you raise it higher.
Frozen Shoulder
Frozen shoulder develops when the tissue surrounding the shoulder joint thickens and tightens, progressively restricting movement. It moves through three distinct stages, and the entire process can take well over a year.
The freezing stage lasts six weeks to nine months. Pain increases gradually, and your range of motion starts shrinking. The frozen stage follows, lasting two to six months. Pain may actually decrease during this phase, but stiffness peaks, making it very difficult to move your arm. The thawing stage is the longest, lasting six months to two years, during which motion slowly returns. People with diabetes, thyroid problems, or a history of shoulder immobilization (from surgery or a sling) are at higher risk.
Shoulder Instability
If the ball of your upper arm bone gets forced out of the shoulder socket, either fully or partially, the joint can become unstable. This usually starts with a sudden injury like a fall or collision. Once it happens once, it’s more likely to happen again. Recurring dislocations cause pain and a feeling of looseness when you raise your arm or move it away from your body, and repeated episodes increase the risk of developing arthritis in the joint over time.
Pinched Nerve in the Neck
Not all left shoulder pain starts in the shoulder. A pinched nerve in the cervical spine (neck) can send pain radiating down into the shoulder, arm, and even the chest. The nerves that branch out from your neck connect directly to your shoulders and arms, so a herniated disc or bone spur pressing on one of these nerves can feel identical to a local shoulder problem.
A key difference: nerve-related shoulder pain almost always affects only one side of the body and often comes with numbness, tingling, or weakness in the arm or hand. Moving your neck, not just your shoulder, tends to change the pain. A provider can compare sensation and reflexes on both sides of your body to help distinguish a neck problem from a shoulder problem.
Referred Pain From the Heart
This is the reason left shoulder pain gets more attention than right. A heart attack can cause sudden pain in the left shoulder, arm, jaw, or teeth with no obvious injury. The pain is “referred,” meaning it originates in the heart but is felt in a different location because of shared nerve pathways.
The distinguishing feature of cardiac referred pain is that it appears suddenly with no physical cause. You didn’t fall, lift something heavy, or sleep in a bad position. The pain is often accompanied by tightness or pressure in the chest, difficulty breathing, and sweating. If you have left shoulder pain that came on for no apparent reason along with any of these symptoms, call 911. This is one situation where the cause of left shoulder pain is genuinely time-sensitive.
Referred Pain From the Spleen
A ruptured spleen can send pain to the left shoulder and left side of the chest, a phenomenon known as Kehr’s sign. This happens because bleeding from the spleen irritates a nerve called the phrenic nerve, which runs from the neck down through the left side of the chest. The brain misinterprets the signal as shoulder pain.
A ruptured spleen typically follows abdominal trauma, like a car accident or a hard blow during contact sports. The shoulder pain often shifts from the abdomen upward after the initial rupture. If you’ve had a recent abdominal injury and develop left shoulder pain, that combination needs emergency evaluation.
How the Cause Gets Identified
A physical exam for shoulder pain involves specific movement tests designed to reproduce your symptoms. In one common test, you hold your arms out to the sides at shoulder height with your thumbs pointing down, then try to lift against resistance. This isolates one of the rotator cuff muscles and reveals weakness or pain from a tear. Other tests involve a provider rotating your arm inward or raising it forward to check for impingement: if the rotator cuff tendons get pinched under the bone during these movements, it confirms the diagnosis.
Imaging comes next if the physical exam suggests a tear, instability, or something beyond simple inflammation. An MRI can show partial and full-thickness tears, while X-rays reveal bone spurs, arthritis, or dislocations. For suspected nerve involvement, a provider will test reflexes and sensation on both sides of the body looking for asymmetry.
The most important initial distinction isn’t between different shoulder injuries. It’s between pain from the shoulder itself and pain referred from somewhere else. Shoulder injuries tend to worsen with specific arm movements and improve with rest. Referred pain from the heart or abdomen appears without a physical trigger, doesn’t change much with shoulder movement, and comes with symptoms that have nothing to do with the shoulder: chest pressure, shortness of breath, abdominal tenderness, or dizziness.