Shoulder pain can be related to heart problems due to a neurological phenomenon known as referred pain. Pain originating from the heart is mistakenly perceived in the shoulder, neck, or jaw. This occurs because the brain interprets vague signals from internal organs as coming from a more familiar location on the body’s surface. Understanding this mechanism is important for recognizing when a common ache might signal a serious cardiac event.
The Neurological Basis of Referred Pain
Referred pain occurs because nerve pathways carrying signals from internal organs share connections with pathways from the skin and musculoskeletal structures. Pain signals travel from the heart via general visceral afferent (GVA) fibers back to the spinal cord. These visceral fibers converge onto the same neurons that receive input from somatic structures like the shoulder and arm.
The brain is accustomed to interpreting signals from these shared neurons as originating from the more densely innervated somatic areas. This misinterpretation projects the stimulus from the heart onto the corresponding dermatomal region of the body surface. The heart’s sensory fibers primarily enter the spinal cord at the T1 to T5 segments, which corresponds to the nerve distribution areas of the chest, left arm, and shoulder.
The convergence of nerve signals at the spinal level explains how pain from a cardiac event can bypass the chest and be felt solely in the shoulder. This shared pathway also explains why the pain can radiate to other areas, such as the neck, jaw, or upper back. Due to this anatomical overlap, the pain felt in the shoulder is perceived as real, even though the source of the problem is the heart muscle itself.
Specific Cardiac Conditions Linked to Shoulder Pain
Referred shoulder pain is a well-documented symptom in two primary cardiac conditions: Myocardial Infarction (MI), or a heart attack, and Angina Pectoris. A heart attack occurs when blood flow to the heart muscle is severely reduced or blocked, leading to tissue death. Angina is temporary chest pain or discomfort resulting from reduced blood flow and oxygen to the heart muscle, often triggered by exertion or stress.
The pain associated with these cardiac events is typically described as a heavy pressure, an uncomfortable squeezing, or a profound ache, unlike the sharp, localized pain of a muscle strain. This discomfort is often diffuse, meaning it is difficult to pinpoint a specific location, and it may radiate down the left arm, though it can affect the right shoulder or both. Crucially, cardiac-related pain does not usually change with movement, position, or rest, which differentiates it from common musculoskeletal shoulder pain.
In contrast, typical shoulder pain from conditions like a rotator cuff injury or arthritis is usually reproducible, meaning it worsens when the joint is moved or pressed in a certain way. Musculoskeletal pain is often sharp, specific to the joint or muscle, and may improve with rest or a change in position. For heart-related shoulder pain, the discomfort may intensify with physical activity or emotional stress because the heart’s oxygen demand increases.
Critical Warning Signs and When to Seek Emergency Care
When shoulder pain is accompanied by certain systemic symptoms, it transforms into a medical emergency requiring immediate attention. The most significant red flags are the sudden onset of severe, unrelenting shoulder discomfort combined with other signs of acute cardiac distress.
Systemic signs include profound shortness of breath (dyspnea), which may feel like an inability to take a deep breath. Other concerning symptoms are unexplained cold sweats (diaphoresis), nausea, or vomiting. A feeling of light-headedness, dizziness, or profound, sudden fatigue that does not resolve with rest are also serious indicators.
If shoulder pain is experienced alongside a crushing pressure in the chest, or if the pain radiates to the jaw, neck, or back, one should immediately call the local emergency services number (e.g., 911). It is important not to drive oneself to the hospital. If the pain is new, persistent, and has any of the aforementioned characteristics, but lacks the acute systemic symptoms, a person should still seek prompt medical evaluation, ideally with a primary care physician, to rule out a developing condition.