Each adult heart muscle cell, called a cardiomyocyte, contains thousands of mitochondria, the tiny structures that turn food and oxygen into usable energy. Scientific reviews estimate about 1,000 to several thousand per cell [6][7]. Measured by space instead of count, mitochondria made up about 23% of human heart muscle tissue in biopsy studies, and reviews describe them as filling at least 30% of each heart muscle cell [3][5].
Key Takeaways
- An adult heart muscle cell holds thousands of mitochondria; published estimates start at about 1,000 per cell.
- In biopsies of human hearts, mitochondria took up about 23% of heart muscle tissue volume. Reviews put them at 30% or more of each heart muscle cell.
- Mitochondria supply more than 95% of the energy (ATP) the heart uses, and the heart stores only a few seconds of reserve energy.
- Smaller mammals with faster heartbeats have even more: up to about 37% of heart muscle volume across 10 species studied.
- Endurance training raised mitochondrial volume in human leg muscle by about 40% in six weeks. Comparable direct data for the human heart are scarce.
Evidence grade: Strong. The figures come from direct electron-microscope measurements of human and animal heart tissue, repeated across studies since the 1980s, and agree with recent scientific reviews.
Mitochondria in Heart Cells at a Glance
| Measure | What studies found | Source |
|---|---|---|
| Mitochondria per adult heart muscle cell | About 1,000 to thousands (estimates vary by method) | [6][7] |
| Share of human heart muscle tissue (biopsies) | 23% mitochondria, 59% contractile fibers, 18% other cell contents | [3] |
| Share of each adult heart muscle cell | At least 30% (review figure) | [5] |
| Range across 10 mammal species, including humans | 22% to 37% of heart muscle volume | [4] |
| Share of the heart's ATP made by mitochondria | More than 95% | [8] |
| ATP turned over by a human heart each day | 15 to 20 times the heart's own weight | [8] |
How Many Mitochondria Are in One Heart Cell?
Most cells in the body contain hundreds to thousands of mitochondria [1]. Heart muscle cells sit at the high end of that range. A 2020 review describes mature heart muscle cells as containing thousands of rounded mitochondria lined up end to end [6]. A 2016 review gives a rounder estimate of about 1,000 mitochondria per heart muscle cell [7].
Why the spread? Counting individual mitochondria is hard. In heart cells they are packed tightly in rows between the contractile fibers, and their size and shape can differ from one area of the cell to another. Different counting methods, species and cell sizes give different totals. That is why most researchers describe heart mitochondria by the share of space they take up, which is easier to measure and compare.
How Much of a Heart Cell Is Mitochondria?
The classic human figure comes from a 1985 study in Circulation Research. Researchers used electron microscopy to measure biopsied human heart tissue and found it was 23% mitochondria, 59% contractile fibers (myofibrils) and 18% other cell contents [3]. In other words, close to a quarter of heart muscle is devoted to making energy.
Reviews that focus on the individual heart muscle cell, rather than whole tissue, put the figure at "at least 30%" of cell volume [5]. The two numbers measure slightly different things, so both are reasonable. Either way, mitochondria are one of the largest components of a heart cell after the fibers that contract.
Smaller hearts, more mitochondria
The same research group later compared heart muscle from 10 species, including humans. Mitochondria ranged from 22% to 37% of heart muscle volume. Each species had its own steady value, and the smallest animals had the highest share [4]. Mitochondrial content tracked heart rate and resting oxygen use, which fits the idea that faster-beating hearts need more energy-producing machinery [3][4].
| Heart muscle sample | Mitochondria (% of tissue volume) |
|---|---|
| Human (biopsy) | 23% |
| Dog | 22% |
| Rat | 28% |
| Hamster | 28% |
| Mouse | 32% |
Figures from Schaper and colleagues, 1985 [3]. The 10-species comparison reported a range of 22% to 37% [4].
Where Mitochondria Sit Inside a Heart Cell
Heart mitochondria are not scattered at random. Studies of heart muscle describe two main groups. Subsarcolemmal mitochondria sit just under the cell's outer membrane. Interfibrillar mitochondria are lined up between the contractile fibers, right next to the machinery that uses their ATP [9].
The two groups also behave a little differently. In rat heart muscle, interfibrillar mitochondria used fuels about 1.5 times faster than those under the membrane [9]. Because heart cells are so tightly packed, mitochondria in adult heart cells move far less than mitochondria in many other cell types [6].
Why the Heart Needs So Many Mitochondria
The short answer is constant demand. Mitochondria make more than 95% of the ATP the heart uses, and a human heart turns over an amount of ATP equal to 15 to 20 times its own weight every day [8]. The heart's stored high-energy reserves would keep it beating for only a few seconds, so energy production has to keep pace with every beat [8]. Heart mitochondria also help regulate calcium, cell signaling and cell survival [8].
We explain the energy side in more detail in why the heart has more mitochondria, including how mitochondria make ATP and which nutrients are involved.
Can the Number of Mitochondria Change?
Mitochondria respond to how much energy a tissue is asked to produce. Most direct human evidence comes from skeletal muscle, because healthy people rarely give heart tissue samples for research. In a 1985 study, 10 adults did six weeks of hard cycling training. Biopsies of their thigh muscle showed that total mitochondrial volume rose by about 40%, while their aerobic capacity per kilogram of muscle rose by about 14% [10].
Whether the heart responds in the same way in healthy adults is much harder to measure, so it is best not to assume the same numbers apply. For training ideas, see the best exercise to increase mitochondria, and for a wider view of the topic read our guide to mitochondrial health.
CoQ10 and Heart Mitochondria
Coenzyme Q10 (CoQ10) is made by your own cells and is a working part of the energy chain inside mitochondria. It acts as a cofactor for ATP production and also has antioxidant activity [11]. The National Center for Complementary and Integrative Health (NCCIH) notes that the body's highest CoQ10 levels are in the heart, liver, kidneys and pancreas [2].
That link has made CoQ10 supplements popular, but the research needs to be read carefully. NCCIH reports that studies of CoQ10 supplements for heart-related outcomes have so far been inconclusive [2]. No research cited here shows that a CoQ10 supplement changes the number of mitochondria in heart cells. Food sources are covered in our guide to CoQ10 foods.
For adults who choose a supplement as part of a general wellness routine, OPA CoQ10 Ubiquinone provides 200 mg of coenzyme Q10 as ubiquinone in one capsule a day, formulated for cellular energy and antioxidant support. Each bottle holds 30 capsules, a 30-day supply. For context, a 2008 safety review that pooled clinical trial data put the observed safe level of CoQ10 at 1,200 mg a day, six times this amount; that review was written by scientists at a company that makes CoQ10 [11].
Safety and Interactions
Learning how many mitochondria your heart has is safe; changing your routine because of it calls for a little care.
- CoQ10 side effects: No serious side effects have been reported. Mild problems such as trouble sleeping or an upset stomach can occur [2].
- Medication interactions: CoQ10 may interact with the blood thinner warfarin and with insulin, and it may not be compatible with some types of cancer treatment [2]. Talk to your doctor or pharmacist before taking CoQ10 if you use any of these.
- Exercise: If you are new to hard endurance training, or have any heart symptoms such as chest pain, fainting or unusual shortness of breath, check with your doctor before starting.
- Pregnancy and breastfeeding: Ask your healthcare provider before taking any supplement.
Frequently Asked Questions
How many mitochondria are in a heart cell?
An adult heart muscle cell contains thousands of mitochondria. Reviews give estimates from about 1,000 per cell upward, and the exact number depends on how they are counted [6][7]. Researchers more often report the share of space they fill: about 23% of human heart muscle tissue and at least 30% of each heart muscle cell [3][5].
What percentage of the heart is mitochondria?
In biopsies of human hearts, mitochondria made up about 23% of heart muscle tissue, next to 59% contractile fibers [3]. Across 10 mammal species the range was 22% to 37%, with smaller animals at the high end [4].
Do heart cells have more mitochondria than other cells?
Heart muscle cells are at the high end. Most cells contain hundreds to thousands of mitochondria [1], while heart muscle cells contain thousands and devote roughly a quarter to a third of their volume to them [3][5][6].
Why does the heart have so many mitochondria?
The heart beats nonstop and keeps only a few seconds of stored energy, so it must make ATP continuously. Mitochondria supply more than 95% of that ATP [8]. Read more in why the heart has more mitochondria.
Are mitochondria in heart cells different from those in other cells?
They do the same basic job, but heart cells have two distinct groups: one just under the cell membrane and one packed between the contractile fibers. In rat hearts, the group between the fibers used fuel about 1.5 times faster [9].
Can you increase the number of mitochondria?
In human leg muscle, six weeks of endurance training raised mitochondrial volume by about 40% [10]. Direct evidence for the human heart is limited, and no research cited here shows that a supplement increases heart mitochondria.
Sources
- MedlinePlus Genetics. Mitochondrial DNA. National Library of Medicine.
- National Center for Complementary and Integrative Health. Coenzyme Q10.
- Schaper J, Meiser E, Stämmler G. Ultrastructural morphometric analysis of myocardium from dogs, rats, hamsters, mice, and from human hearts. Circ Res. 1985.
- Barth E, Stämmler G, Speiser B, Schaper J. Ultrastructural quantitation of mitochondria and myofilaments in cardiac muscle from 10 different animal species including man. J Mol Cell Cardiol. 1992.
- Piquereau J, Caffin F, Novotova M, et al. Mitochondrial dynamics in the adult cardiomyocytes: which roles for a highly specialized cell? Front Physiol. 2013.
- Li A, Gao M, Jiang W, Qin Y, Gong G. Mitochondrial dynamics in adult cardiomyocytes and heart diseases. Front Cell Dev Biol. 2020.
- Gottlieb RA, Bernstein D. Mitochondrial remodeling: rearranging, recycling, and reprogramming. Cell Calcium. 2016.
- Kolwicz SC Jr, Purohit S, Tian R. Cardiac metabolism and its interactions with contraction, growth, and survival of cardiomyocytes. Circ Res. 2013.
- Palmer JW, Tandler B, Hoppel CL. Biochemical properties of subsarcolemmal and interfibrillar mitochondria isolated from rat cardiac muscle. J Biol Chem. 1977.
- Hoppeler H, Howald H, Conley K, et al. Endurance training in humans: aerobic capacity and structure of skeletal muscle. J Appl Physiol. 1985.
- Hidaka T, Fujii K, Funahashi I, Fukutomi N, Hosoe K. Safety assessment of coenzyme Q10 (CoQ10). Biofactors. 2008.
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
