CHIEF’S CORNER: HOT BLOODED?

By Fire Chief Sam DiGiovanna

July 25, 2025 (San Diego) -- Warm temperatures can have a surprisingly complex impact on your blood and cardiovascular system. Here's how your body responds when the heat rises. Heat does not literally “thicken” the blood, but dehydration from heat can make your blood more concentrated, which might feel similar in effect.

Sweating leads to fluid loss. If you don’t replace that lost fluid, your body becomes dehydrated. Dehydration reduces plasma (the liquid part of your blood), so your blood becomes more concentrated. This can increase blood viscosity, which can strain the heart and raise the risk of issues like clots, especially in people with heart disease, stroke history, or clotting disorders.

What Happens to Your Blood in Warm Weather

• Vasodilation: Your blood vessels, especially near the skin, widen to help release heat. This lowers vascular resistance, which can cause blood pressure to drop.
• Increased Heart Rate: To compensate for lower pressure and maintain circulation, your heart may beat faster.
• Dehydration Risk: Sweating leads to fluid loss, which reduces blood volume. Less volume means less pressure, and that can cause dizziness or fainting.
• Electrolyte Imbalance: Along with fluids, you lose sodium and potassium through sweat. These electrolytes are vital for nerve and muscle function, including your heart.
• Strain on the Heart: The combination of vasodilation, dehydration, and electrolyte shifts can make your heart work harder, especially if you have pre-existing conditions.

Who’s Most at Risk

• Firefighters
• People with heart disease, high blood pressure, or kidney conditions
• Those taking medications like diuretics, beta blockers, or ACE inhibitors
• Older adults and young children
• Anyone working or exercising outdoors in the heat

Tips to Stay Safe

• Hydrate regularly—don’t wait until you’re thirsty
• Avoid peak heat hours (10 a.m. to 4 p.m.)
• Wear breathable clothing and use sunscreen
• Monitor blood pressure if you’re sensitive to heat or on medication
• Watch for warning signs like dizziness, rapid pulse, or muscle cramps
• Watch salt intake

Eat Heart-Friendly Summer Foods

• Watermelon – hydrates and contains heart-friendly lycopene
• Berries – rich in antioxidants
• Tomatoes, avocados, cucumbers – cooling and anti-inflammatory
• Grilled fish (like salmon or tuna) – high in omega-3s

“Heat may rise, but your cool is in your hands!”

*Note: The information in this article was compiled from various sources. These suggestions are not a complete list of every preventative or loss control measure. The information is not intended to replace additional safety manuals or the advice of another qualified professional(s). We make no guarantee of results from use of this information. We assume no liability in connection with the information nor the suggestions.