Why do humans (but not turtles) benefit from rapid chest compressions in CPR?

Short answer: Turtles have a shell, so chest compressions aren’t really possible. But it’s more interesting than that!

Medium answer: CPR in adult humans should be performed at a rate of 100-120/min. By contrast, turtles can survive at heart rates as low as 1 beat every 5-10 minutes. Human heart muscle is oxygenated by dedicated blood vessels (coronary vessels), whereas turtle heart muscle is directly oxygenated by the blood in the heart. The coronary arteries require a pressure gradient to fill, which can be achieved only by multiple compressions in a row. Therefore, the primary focus of human CPR focuses on keeping the heart perfused via compressions, whereas turtle CPR can focus more on oxygenation.

The adult out-of-hospital Chain of Survival. Source.

While reading about painted turtle physiology yesterday, I came across a line from Donald Jackson’s review: “Under [anaerobic and hypoxic] conditions, the turtle’s heart rate can be as low as 1 beat every 5–10 min.” This didn’t square at all with my understanding of human CPR, in which 30 chest compressions should be performed for every 2 rescue breaths.

The rationale behind 30 compressions is that a longer stretch of uninterrupted compressions leads to increased time of adequate blood flow (perfusion) to the heart muscle (myocardium). When spontaneous circulation stops, there is no longer a pressure gradient between arteries and veins. As chest compressions begin, this gradient begins to build up again due to resistance from arterioles. The heart relies on this pressure gradient to be perfused – during diastole (when the heart relaxes), back pressure from the arterioles allows some blood to flow backwards towards the heart. During this time, the aortic valve that connects the left ventricle to the aorta is closed, so blood will instead flow to the coronary vessels (blood vessels that supply the heart, whose entrances are at the aortic root). However, if there is no pressure gradient due to loss of spontaneous circulation (or the cessation of compressions), no blood will flow into the coronary arteries. This pressure gradient actually takes a few compressions to build up – as seen in the diagram below. There is actually a pretty substantial reserve of oxygen in the blood, so distributing that reserve is usually more important than giving more oxygen.

Figure 2 from Cunningham et al. shows that prolonged interruptions in chest compressions leads to a decrease in myocardial perfusion pressure that takes a while to build up again.

By contrast, turtle hearts are three-chambered and lack significant coronary circulation. Similar to fish hearts, turtle hearts are composed primarily of spongy myocardium that receives direct perfusion from the blood within. In addition, turtle hearts lack a complete septum between the left and the right ventricle. This contrasts with humans in which, the left and right ventricles are completely separated. Thus, turtle hearts can support both left-to-right shunts to better perfuse the body during exercise, as well as a right-to-left shunt to increase digestion and gastric acid secretion.

Therefore, “turtle CPR” focuses more on oxygenation. For those that ever have to resuscitate turtles, some pearls are:

  1. Turtle CPR is all about the airway. Small pieces of food can get stuck resulting in choking. In addition, turtles can indeed inhale water and drown – even in shallow water! This is despite the fact that turtles can oxygenate in water via cloacal (combined GI/GU tract) breathing…
  2. Get the turtle out of water
  3. Elevate the hind end of the turtle (to let gravity get rid of water)
  4. Straighten, then bend the front legs of the turtle. This may help squeeze out some more water from the lungs.
  5. Take the turtle to a vet afterwards! They will give oxygen (and usually antibiotics)

Also, everyone can benefit from a basic understanding of how to perform CPR. Dr. Glaucomflecken makes an excellent pitch here. And for those short on time to formally learn – remember to push hard and fast on the center of the chest (100-120/min, about the speed of Stayin’ Alive). Rescue breaths do not lead to better survival if you are not EMS trained. If you don’t believe that- even Walter White says so (don’t follow his example though -instead lock your elbows, use your core, and don’t hang out with psychotic drug lords)!


  1. https://cpr.heart.org/en/resources/cpr-facts-and-stats/out-of-hospital-chain-of-survival
  2. Jackson DC. How a Turtle’s Shell Helps It Survive Prolonged Anoxic Acidosis. News Physiol Sci. 2000 Aug;15:181-185. doi: 10.1152/physiologyonline.2000.15.4.181. PMID: 11390905.
  3. Cunningham LM, Mattu A, O’Connor RE, Brady WJ. Cardiopulmonary resuscitation for cardiac arrest: the importance of uninterrupted chest compressions in cardiac arrest resuscitation. Am J Emerg Med. 2012 Oct;30(8):1630-8. doi: 10.1016/j.ajem.2012.02.015. Epub 2012 May 23. PMID: 22633716.
  4. Farmer CG, Hicks JW. The Intracardiac Shunt as a Source of Myocardial Oxygen in a Turtle, Trachemys scripta. Integr Comp Biol. 2002 Apr;42(2):208-15. doi: 10.1093/icb/42.2.208. PMID: 21708712.
  5. Farmer CG. On the evolution of arterial vascular patterns of tetrapods. J Morphol. 2011 Nov;272(11):1325-41. doi: 10.1002/jmor.10986. Epub 2011 Jun 27. PMID: 21710654.
  6. https://farmer.biology.utah.edu/Hunt%20and%20Shunt.html
  7. https://crazycrittersinc.com/cpr-in-turtles-and-tortoises-yes-they-can-choke-and-drown/
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