Research shows that heart rate significantly affects how well an animal’s heart relaxes and fills with blood during ultrasound exams under anesthesia. According to Gram Research analysis of a 2026 study, when heart rate drops too low, the heart’s diastolic function—its ability to relax between beats—becomes markedly worse in both rats and mice. The study identified optimal heart rate ranges for accurate measurements: 390-450 beats per minute for rats and 450-480 or 510-550 beats per minute for mice. These findings help researchers get more reliable data when studying heart disease in animal models.
Scientists studied how heart rate affects heart function in healthy and sick animals using ultrasound imaging. They found that when heart rate drops too low during anesthesia, the heart’s ability to relax and fill with blood gets worse. The research shows there are specific heart rate ranges where measurements are most accurate for both rats and mice. According to Gram Research analysis, understanding these ranges helps veterinary researchers get better data when studying heart disease in animal models, which could eventually improve treatments for human heart problems.
Key Statistics
A 2026 research article in Frontiers in Physiology found that in 22 rats (11 healthy and 11 with heart failure), low heart rates caused marked decreases in diastolic dysfunction—the heart’s ability to relax and fill with blood—in both healthy and diseased hearts.
Research on mice and rats under anesthesia identified optimal heart rate measurement windows of 390-450 beats per minute for rats and 450-480 or 510-550 beats per minute for mice to ensure accurate ultrasound readings of heart function.
A 2026 study comparing healthy rats to those with post-heart-attack failure found that while heart rate changes had minor effects on how hard the heart contracted, bradycardia (slow heart rate) easily caused diastolic dysfunction in both species.
The Quick Take
- What they studied: How different heart rates affect the heart’s pumping ability in healthy animals and those with heart failure, measured using ultrasound
- Who participated: 22 male rats total—11 healthy rats and 11 rats with heart failure created by blocking blood flow to part of the heart. Also included mice with a different type of heart failure
- Key finding: When heart rate dropped too low, the heart couldn’t relax and fill properly in both rats and mice. The best heart rate ranges for accurate measurements were 390-450 beats per minute for rats and 450-480 or 510-550 beats per minute for mice
- What it means for you: For researchers studying heart disease in animals, using the right heart rate ranges during ultrasound exams gives more reliable results. This helps scientists better understand how treatments work before testing them in humans
The Research Details
Researchers used two different animal models to study heart function. First, they created heart failure in rats by tying off a blood vessel in the heart, similar to a human heart attack. Second, they created a different type of heart failure in mice using a special diet combined with a drug that blocks a protective substance in the body. All animals were put under anesthesia and had their hearts examined with ultrasound (echocardiography) while their heart rates were controlled by adjusting the depth of anesthesia. The team measured how well the heart pumped blood out and how well it relaxed and filled with blood at different heart rates.
When scientists study heart disease in animals, they need accurate measurements to know if a treatment is working. Heart rate affects how the heart functions, so researchers need to know which heart rates give the most reliable ultrasound readings. This study identifies those ‘sweet spot’ heart rates so future research can be more accurate and trustworthy
This is original research published in a peer-reviewed journal (Frontiers in Physiology). The study used two different animal models and two different ways of creating heart failure, which strengthens the findings. However, the sample size was relatively small (11 rats per group), and the findings are specific to animals under anesthesia, so results may not directly apply to awake animals or humans
What the Results Show
The most important discovery was that low heart rates (bradycardia) caused problems with how the heart relaxed and filled with blood in both rats and mice. When heart rate dropped, the diastolic function—the heart’s ability to relax between beats—got noticeably worse. This happened in both healthy animals and those with heart failure. In contrast, the heart’s ability to pump blood out (systolic function) stayed relatively stable across different heart rates in rats, but decreased in mice when heart rate dropped. The researchers found that heart rate changes had only minor effects on how hard the heart contracted in normal conditions, but the relaxation phase was much more sensitive to heart rate changes.
The study identified specific heart rate ranges where measurements were most reliable: 390-450 beats per minute for rats and 450-480 or 510-550 beats per minute for mice. These ranges represent the ‘practical measurement windows’ where researchers can get the most accurate ultrasound readings. The findings were consistent across both healthy animals and those with heart failure, suggesting these ranges work well regardless of the heart’s condition
Previous research suggested that heart rate affects heart function, but this study provides specific, practical guidance for researchers. It confirms that low heart rates are problematic for measuring diastolic function and establishes exact heart rate ranges for reliable measurements. This builds on earlier work by being more precise about which heart rates to use during animal studies
The study used only male rats and mice, so results may not apply to females. The animals were under anesthesia, which affects how the heart works, so findings may not reflect how the heart functions in awake animals. The sample size was small (11 rats per group), which limits how confident we can be in the results. The study focused on specific types of heart failure in animals, so applying these findings to other heart conditions or to humans requires caution
The Bottom Line
For researchers using ultrasound to study heart function in rats and mice under anesthesia: maintain heart rates of 390-450 bpm for rats and 450-480 or 510-550 bpm for mice to get the most accurate measurements. Avoid letting heart rate drop too low, as this causes unreliable readings of how well the heart relaxes. These recommendations are based on solid experimental evidence but apply specifically to anesthetized animals
This research is most relevant to veterinary researchers, scientists studying heart disease in animal models, and pharmaceutical companies testing new heart medications in animals. It’s less directly relevant to the general public, though the findings may eventually improve how heart disease treatments are developed and tested
These are guidelines for immediate use in research settings. Researchers who follow these heart rate recommendations should see improved accuracy in their measurements right away. The long-term benefit comes from more reliable animal studies, which could lead to better heart disease treatments for humans over years or decades
Frequently Asked Questions
Why does heart rate affect how well the heart works during ultrasound exams?
Heart rate directly influences how the heart relaxes and fills with blood between beats. When heart rate drops too low during anesthesia, the heart’s relaxation phase (diastolic function) becomes impaired, making ultrasound measurements less accurate. This is why researchers need to maintain specific heart rate ranges for reliable data.
What heart rate should be maintained during animal heart ultrasounds?
For rats under anesthesia, maintain 390-450 beats per minute. For mice, use 450-480 or 510-550 beats per minute. These ranges ensure the most accurate ultrasound measurements of heart function. Heart rates below these ranges cause the heart to relax poorly, producing unreliable results.
Does this research apply to humans with heart disease?
This study focused on anesthetized animals, so direct application to awake humans is limited. However, the findings help researchers better study heart disease in animal models, which eventually improves how new heart treatments are developed and tested before human trials.
Why is diastolic function more affected by heart rate than systolic function?
The study found that how hard the heart pumps (systolic function) stays relatively stable across heart rates, but how well it relaxes (diastolic function) is much more sensitive to changes. Low heart rates give the heart less time to relax properly, causing diastolic dysfunction in both healthy and diseased hearts.
Want to Apply This Research?
- For researchers: track the heart rate during each ultrasound measurement and record whether it falls within the recommended range (390-450 bpm for rats, 450-480 or 510-550 bpm for mice). Note any measurements taken outside these ranges as potentially less reliable
- Adjust anesthesia depth during animal ultrasound exams to maintain heart rate within the optimal ranges identified in this study. Set alerts if heart rate drops below the minimum recommended rate to prevent unreliable measurements
- Create a log of heart rate ranges used during each ultrasound session and correlate this with measurement quality. Over time, this helps identify which specific heart rate ranges within the recommended windows give the most consistent results for your particular equipment and technique
This research describes how heart rate affects ultrasound measurements in anesthetized laboratory animals and is intended for researchers and veterinary professionals. The findings do not directly apply to human heart disease diagnosis or treatment. If you have concerns about your heart health, consult a qualified healthcare provider. This study was conducted in controlled laboratory settings with specific animal models and may not reflect how the heart functions in awake animals or humans.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.