So, my first stop in trying to answer this question was on Johns Hopkins website, but they are way too vague about the procedure, especially the use of a cardiopulmonary bypass machine. The only mention of the CPBM is this:

“The surgeon will put tubes into your chest so that your blood can be pumped through your body by a heart-lung (cardiopulmonary bypass) machine while your heart is stopped and replaced.”

So, I tried several more websites, such as WebMD, the Mayo Clinic, Medline Plus, the University of Rochester Medical Center, the University of Pittsburgh Medical Center, and a few others, before I altered my search. Next, I started looking for information specifically on CPBM.

The first article I came to was from the National Center for Biotechnology Information. We’ll call this exhibit 1. This gave a much better description of how the CPBM works. It tells me single-stage cannulae are used during most open-heart surgeries, which involves two cannulae being inserted into the superior and inferior vena cava and joined by a “Y-piece”. Now I searched “Y-piece”, “Y-piece heart surgery”, and finally found something when I searched “Y-piece cannula”. From what I understand, this is just a triple line IV that feeds into a single catheter, but I can’t be sure, the Wikipedia page is a little vague, I’m going off the picture on the Wiki page. Luckily, this is irrelevant.

This page then says that Dual-stage cannulae are used for most closed-heart procedures. Now, other research tells me that the advantage of single-stage is speed and fewer incisions. The downside is that single-stage cannot stop ALL blood from pumping to the heart. What confused me is that the above website says that two cannulae are used for single-stage, but this website, which we’ll call exhibit 2, says that dual-stage also uses two cannulae. Further the sites disagree on how many cannulae are used for dual stage. Exhibit 1 says that 1 cannula is used for dual stage, while the other website says 2. Logic would tell me the first website made a typo, but I have no idea what to make of it. So, I am not sure what’s up with that, but I am hoping that is irrelevant to my question. But they don't specifically talk about transplant surgery.

I understand that during heart surgery, (but maybe not heart transplant surgery, unclear as to whether it is sutured in a transplant) the arterial cannula is stitched into the aorta, as this INCREDIBLE video shows. Then the venous cannula is inserted into the right atrium, passes through the diaphragm, and into the inferior vena cava just behind the liver, again, as shown in this video. Next, the aortic root vent is placed on the ascending aorta, between arterial and venous cannula, in order to push cold potassium into the heart in order to stop it as shown here. Then, sometimes another cannula, the coronary sinus catheter, goes through the free wall of the right atrium and is inserted “by feel” (which seems nuts to me) into the coronary sinus, as shown here. Now, I believe he answers my question here when he talks about clamping the aorta. He says that will stop the blood from flowing to the heart. He says the only way out will be down the heart arteries. But I don’t understand how.

Next, I found this AMAZING video of a computer-animated heart suspended in space undergoing a heart transplant.

Here’s what I have learned. There are several major blood vessels that go to/from the heart that need to be accounted for. First there is the aorta, which is the main artery that pumps blood to the rest of the body. A cannula is inserted into the aorta. Then there is the superior and inferior vena cava. The superior vena cava carries blood from the head, neck, arms, and chest to the heart, while the inferior vena cava brings blood from the legs, feet, abdomen, and pelvis to the heart. Both will receive a cannula. As I understand, next, the aorta is clamped distil to the cannula. Then, cold cardioplegia is pushed through the aortic cannula, stopping the heart from beating for removal. Next, cable snares are placed around both parts of the vena cava, distal to the cannulae in order to stop blood flow. Following this, the superior and inferior vena cava are severed proximal to the heart, making sure to leave a decent rim of tissue to which the donor heart can be attached. Next the ascending aorta is severed proximal to the clamp, followed by the pulmonary artery. Then, the left atrium is divided making sure to leave the four pulmonary veins “attached to a cuff of left atrium” where the donor heart can be attached.

At this point the diseased or failing heart is removed. Then, the video says the new heart is “brought into the field and examined for any heart defects”, which I hope was ALSO checked before the other heart was removed. I can’t imagine too many surgeons just accept a heart without ever looking at it, then remove a patient’s heart, only to find out the donor heart is no good. So I presume this is the last of many checks. Anyways, the left atrium is then sewed together. Following that, the ascending aorta is sutured, and the clamp removed, hopefully restoring function to the heart. Then, the pulmonary artery, inferior vena cava, then superior vena cava are all sutured to the new heart. Next, the patient is slowly weaned off bypass, and the rest is irrelevant.

So, my question is, once the heart is removed, why does blood not pour out of the hole left where the left atrium was, and the pulmonary artery? Neither of these are clamped. The pulmonary veins all empty into the left atrium. So, how does the CPBM continue circulation when there is a gaping hole where four large veins empty, and an even larger artery? I’m obviously missing something. It just seems necessary to clamp the pulmonary veins and artery..

I hope this is enough detail. I apologize for being so vague before.

  • 1
    Your question seems unclear to me. Are you misunderstanding that nutrients and oxygen used by lung tissue does not come from the pulmonary vasculature but instead from the bronchial vasculature? The bronchial arteries arise from the thoracic aorta.
    – Ian Campbell
    Commented Jun 13, 2022 at 18:05
  • 2
    This is very long and fairly unclear to me. Commented Jun 13, 2022 at 19:06
  • @IanCampbell I think they're asking what happens to blood in the pulmonary circulation (that is, between pulmonary artery and pulmonary vein) during bypass. I don't know if they're thinking specifically about the blood that fills that space, but perhaps they're forgetting that if the heart is stopped no new blood is going down that path anyways, and that this is cardiopulmonary bypass and the whole pulmonary circulation is being bypassed as well.
    – Bryan Krause
    Commented Jun 14, 2022 at 3:20
  • The left atrium and pulmonary artery seem to remain unplugged, so wouldn't the blood being pumped by the CBPM just seep out of these gaping holes? Commented Jun 14, 2022 at 3:23
  • 1
    Where would the blood you envision flowing from the left atrium come from? There is no blood in the pulmonary circulation. And I agree with @anongoodnurse that the post is long and unclear. You could probably delete 3/4ths of it, focus solely on the question at hand, and get better answers because more people would actually read it. Right now it's a big wall of text that many people will just skip.
    – Carey Gregory
    Commented Jun 14, 2022 at 4:05

1 Answer 1


"Cardiopulmonary bypass" means the heart (cardio) and lungs (pulmonary) are skipped/bypassed.

Blood from the body is collected where it returns to the heart, in the vicinity of the right atrium (via the vena cavae).

Blood is oxygenated (and often cooled) within the machine, and pumped into the aorta where it flows to the rest of the body.

The heart itself is fed with cardioplegia solution through the coronary arteries.

Since the functions of the heart and lungs are performed by the machine, no circulation through the pulmonary vasculature or heart is needed.

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