5 ways the human heart responds to cold weather

Beyond prompting warm clothing, hot drinks and a plethora of winter-based activities throughout Cleveland, cold weather triggers a host of physiological changes, affecting major organs and muscles and activating survival responses we may barely notice. 

To learn how cold weather impacts the human body, we spoke with Sanjay Rajagopalan, MD, director of the Cardiovascular Research Institute at Case Western Reserve University School of Medicine, who shared five ways the heart responds to cold weather.

Read on to hear Rajagopalan's insights. Then, discover ways you can stay safe as temperatures dip in Cleveland. 

Answers have been edited for clarity and length. 

1. Blood vessels tighten and blood pressure rises. 

When exposed to cold, the body activates the sympathetic nervous system, similar to a fight-or-flight response. Blood vessels near the skin constrict to preserve heat, which can raise blood pressure by 5–30 mmHg. This increased resistance causes the heart to work harder, raising its oxygen demand and placing extra strain on the cardiovascular system.

2. The heart’s rhythm and workload change. 

Cold exposure can initially increase heart rate due to a surge of stress hormones such as adrenaline. However, with prolonged exposure or cold-water immersion—the heart may paradoxically slow down. At the same time, cold conditions thicken the blood and increase platelet activity, creating a higher risk for arrhythmias, ischemia and heart attacks.

3. Existing heart conditions are exacerbated.

For individuals with hypertension, heart failure or coronary artery disease, cold weather can be especially dangerous. Vasoconstriction raises blood pressure and reduces blood flow to the heart muscle, potentially triggering chest pain or heart attacks. In heart failure patients, increased afterload can lead to fluid buildup in the lungs, worsening shortness of breath and increasing the risk of dangerous heart rhythms.

4. Exercise feels harder than usual. 

Even healthy individuals experience greater cardiovascular strain when exercising in cold weather. Narrowed blood vessels increase the resistance against which the heart must pump, while exercise simultaneously raises heart rate and oxygen demand. Together, these effects push the heart closer to its physiological limits, increasing the risk of rhythm disturbances—especially during intense or sudden activity.

5. Certain behaviors become riskier in cold temperatures.

Cold weather can blunt thirst, making dehydration more common. This leads to thicker blood and a higher risk of clot formation. As a result, sudden exertion—such as shoveling snow or starting intense exercise without warming up—can cause abrupt spikes in blood pressure and stress hormones, raising the risk of heart attacks and dangerous arrhythmias, particularly in older adults or those with chronic conditions like diabetes or peripheral vascular disease.