1. How Far a Giraffe's Head Moves When It Bends Down to Drink
To drink water, a giraffe spreads its legs and bends its neck significantly to lower its head. It is said that the head drops by 3 to 5 m (about 10 to 16 ft) before drinking, which presents a major challenge for blood flow within the body [7]. When the head is high, blood must be pushed upward. When the head is low, blood must not pool too much in the head. These two opposite problems coexist in one body. Let us first look at the problem of the high head.
2. Why Pumping Blood Up a Tall Neck Takes So Much Pressure
A water tank on a building’s roof requires a strong pump to deliver water to high places. The higher the place, the stronger the pump must be. Blood also has weight, so pushing it upward takes pressure. Since the head is more than 2 m (about 6.5 ft) higher than the heart, the heart must provide enough pressure to push blood up that height. Research indicates that for every 1 m (about 3.3 ft) of height, an additional blood pressure of 77 mmHg is required at the level of the heart [1]. mmHg is the unit for blood pressure. A paper calculated the pressure of the blood column in the neck arteries at a height of about 2 m (about 6.5 ft), finding it equivalent to about 155 mmHg (nearly equal to 77 × 2) [2]. This is a calculated value based on the paper’s model, and actual values vary depending on the individual and conditions. We used a pump analogy, but blood vessels are more complex than water pipes. Here, we only extract the basic principle that pressure is needed for the height.
3. Why Giraffes Have Such High Blood Pressure, and Why It Is Not an Illness
Giraffe blood pressure is reported to average 200 to 250 mmHg at the level of the heart [1]. This is more than twice that of many mammals. Another researcher explains that a giraffe is about 220/180, while the human standard is about 110/70 [3]. Materials from the Fukuoka City Zoological Garden list the average maximum blood pressure as 260 mmHg [4], so numbers vary by source. It is best to remember it as "about twice that of humans" within a range. While these numbers would be worrying for a human, an explanation from the Japan Heart Foundation states that giraffes are not suffering from hypertension, but that this is a necessary mechanism to send sufficient blood to the brain at the end of the neck [5].
4. How a Giraffe's Heart Makes High Pressure With Thick Walls Instead of a Huge Size
One might think a heart that produces such strong pressure must be huge. However, research reports that this is not the case. The heart of a 1-ton giraffe weighs about 10 kg (about 22 lbs) [5]. While this number seems heavy, it is reported that the ratio to body weight is similar to that of other mammals [6]. A key feature is the thick wall of the left ventricle (the chamber that sends blood to the whole body), and the cavity inside it is small. Thanks to the thick wall, the burden on the wall is kept at a level similar to other mammals. As a result, the amount of blood sent out in one beat is relatively small, and the total amount of blood the heart outputs appears to be kept low [6].
5. How a Giraffe's Long Legs Reduce the Heart's Workload
Giraffes have long legs as well as long necks. The length of the legs seems to be a help, not a hindrance, to the heart’s burden. In a 2025 study, the energy used by the giraffe’s left ventricle was about 16% of the total body metabolism at rest. For a mammal of the same weight with a short neck, it is about 9%. If there were no long legs and the same height were achieved by neck length alone, it is estimated to be about 21% [1]. The 21% figure is an estimate based on assumptions, not a measured value. The explanation is that because the legs are long, the giraffe can be tall without making the neck excessively long, preventing the heart’s work from increasing too much.
6. What Happens to Blood Pressure and Blood in the Neck When the Head Is Lowered
When the head is lowered, blood pools in the thick veins of the neck, and it is said that the amount exceeds 1 liter. As a result, the blood pressure at the level of the heart temporarily drops [3]. When the head is raised again, the pooled blood rushes back to the heart, and the heart pumps it out strongly. A 2025 experiment on drinking giraffes, known to us only through its abstract (summary), reports that "central blood pressure" dropped when the head was lowered, which is the opposite of what many people expect. It also reports an unexpected result: the act of drinking itself raises blood pressure back to pre-drinking levels [7]. Researchers speculate that the water being swallowed may act on the thick veins in the neck. The fine differences in measurement locations and indicators cannot be confirmed from the abstract alone.
7. How Vein Valves and the Net of Vessels Protect a Giraffe's Brain
Japanese materials explain that there are "venous valves" at intervals in the neck veins to prevent backflow, and a mesh-like mass of blood vessels called the rete mirabile (wonder net) at the back of the head acts as a buffer [5]. The Fukuoka City Zoological Garden also lists the rete mirabile as a mechanism to prevent sudden blood pressure changes when lowering the head [4]. However, the extent to which the rete mirabile is effective varies by source. The 2025 study reports that the arteries of the brain can tighten in response to blood pressure, and this response may help protect the brain [7]. It is thought that multiple mechanisms work together, but the division of labor among them is still under research.
8. How to Test Suction Height With a Straw Experiment
You can try an experiment with a straw. Try to see how high you can lift the end of the straw from the water surface in a cup and compare how the sucking force feels. As the height increases, you should need more force to suck. If you see a giraffe drinking at a zoo, watch how it spreads its legs, bends its neck, and raises its head. Does it move slowly? There may be a reason. The Japan Heart Foundation and the Fukuoka City Zoological Garden have explanations about giraffe blood pressure and circulation, in Japanese.