Pain in the left shoulder or arm is a classic symptom of a myocardial infarction, or heart attack, yet it is far more often caused by common musculoskeletal issues. The challenge for the average person lies in distinguishing between a harmless muscle strain and a potentially life-threatening cardiac event. Understanding the body’s wiring and the specific characteristics of the pain can provide clarity and guide the correct response. Recognizing the subtle warning signs can be the difference between a minor delay and a dangerous outcome.
The Connection Between Heart Events and Shoulder Pain
The heart and the left shoulder share a connection through the nervous system that makes the shoulder a common site for referred pain during a cardiac event. When a blockage in a coronary artery reduces blood flow to the heart muscle, the resulting distress can manifest as discomfort radiating outward from the chest. This is why the pain of a heart attack frequently spreads to the left arm, jaw, neck, or back.
While the most widely recognized heart attack symptom is chest discomfort, the pain can sometimes appear to be isolated in the shoulder or arm, which is known as an atypical presentation. More common in certain groups, including women, the elderly, and individuals with diabetes, symptoms are often more subtle. For women, this may include pain in the back, jaw, or shoulder, accompanied by symptoms like nausea or unusual fatigue.
Diabetic patients may experience a “silent” heart attack, where nerve damage called neuropathy can blunt the pain signals. In these cases, the only noticeable symptoms might be shortness of breath, a cold sweat, or unexplained discomfort in the arm or shoulder.
How Referred Pain Works
This occurs because the sensory nerves from the heart and the sensory nerves from the left arm and shoulder enter the spinal cord at similar levels. The central nervous system then processes these signals and perceives them as originating from the somatic, or body surface, area instead of the internal organ.
When a heart attack causes pain signals to flood these shared pathways, the brain is essentially confused about the true source. Since the brain is more accustomed to receiving pain signals from the skin and muscles, it misinterprets the heart’s distress as a musculoskeletal issue in the shoulder or arm. This convergence-projection theory explains why the pain of a heart attack can be felt anywhere along the distribution of the spinal nerves that share this common pathway. It is this neurological overlap that transforms a cardiac issue into what feels like a shoulder problem.
Identifying the Difference Between Cardiac and Muscle Pain
Differentiating between cardiac-related pain and common musculoskeletal (MSK) pain depends on the characteristics of the discomfort and accompanying symptoms. Musculoskeletal pain in the shoulder, such as from a rotator cuff injury or strain, typically worsens with movement or specific positioning of the arm or shoulder joint. This type of pain is often described as sharp, localized, and may be tender to the touch, especially after a physical activity or injury.
In contrast, shoulder pain that is cardiac in origin usually presents as a dull ache, heaviness, or a crushing or squeezing sensation that is not affected by moving the shoulder or arm. The pain tends to persist for more than a few minutes and will not improve with rest or changes in position. A key differentiating factor is the presence of other systemic symptoms, which are almost never present with a simple muscle strain.
Cardiac pain is frequently accompanied by other warning signs, including shortness of breath, cold sweats, unexplained nausea, or lightheadedness. The pain may also radiate to multiple locations simultaneously, such as the jaw, neck, and back. If the shoulder discomfort is brought on by physical exertion or emotional stress and subsides with rest, it may be a sign of angina, which indicates reduced blood flow to the heart.
When to Seek Emergency Medical Attention
Any new or unexplained left shoulder pain, especially when accompanied by other symptoms, requires immediate emergency attention. Call 911 or your local emergency services if the shoulder pain is sudden, severe, and is coupled with systemic symptoms like chest pressure, difficulty breathing, or profuse sweating. Do not attempt to drive yourself or the person experiencing the symptoms to the hospital.
Immediate medical intervention is time-sensitive, as delaying care can lead to permanent damage to the heart muscle. If there are no known allergies or contraindications, emergency services may advise chewing a standard-dose aspirin (325 mg) to help reduce blood clotting while waiting for help to arrive. If the pain is persistent, lasting more than a few minutes, or if it comes and goes but does not resolve with rest, it must be treated as a potential emergency.