Why and how does the body reject a heart transplant?

Organs are foreign. Transplanted organs are treated by the body like foreign invaders (infections). All solid organs transferred between humans are rejected by the immune system of the host. The one exception is identical twins. The rejection process can be halted in most cases with the use of powerful anti-rejection drugs that recipients are given for the life of the graft.
It's "foreign" Every cell in your body has a "label" (antigens) that identifies it as a part of you. A transplanted organ has cells with different "labels" (the donors') so your immune system does not recognize those cells as being part of you and assumes that they are a threat to you (bacteria, virus, cancer cell, etc.) and destroys them by use of chemicals (anti-bodies) or by literally consuming them.
Rejection. Your body rejects the heart transplant because it recognizes the tissue as foreign. Immune cells invade the foreign tissue and can start to destroy it which can weaken the heart and make it fail. After the transplant you take special medicines to help prevent rejection, however, these medicines can also weaken your immune system.

Related Questions

Why is heart transplant difficult?

Donor shortage. Heart failure patients are waiting many months for a matching donor heart after being listed as a suitable candidate.
Medical Complexity. In order for the best results to help the most needy patients, selection of both donor hearts and recipients with end stage cardiac disease is complex. It is also essential that the recipient becomes their own health advocate, and be responsible to take their anti-rejection medications and adhere to the follow-up regimen of the transplant program.

Who did the first heart transplant?

1967. In 1967 the first heart transplant was done by christiaan barnard. Thousands are done in the the world each year with fairly good success.
Barnard. The first one in a human was done by dr. Christian barnard in capetown South Africa in 1967.

Why do you need a heart transplant?

Weak heart muscle. If the heart muscle gets very weak for whatever reason, it may not be able to pump the blood adequately. Therefore if the problem is severe enough and does not improve with medication, sometimes they only treatment left is to remove the diseased heart and tranplant a healthy heart.
Heart failure. When there are proper indications of an absolutely failing heart on major medications, and perhaps with an lvad (left ventricular assist device)in place, a person will be considered and "listed". The surgery requires heart lung machine support of the recipient while their heart is removed and the donor heart is sewn in place.

Can you describe a heart transplant?

Yes. For people you have the most severely damaged hearts a transplant involves removng the heart and replacing it with a donor heart. Multiple heart attacks, and viral damage to the heart muscle are the most common causes. The supply of donors, usually from severe head trauma is very limited, limiting the number of transplants that can be performed. It is a procedure of last resort.
Yes. The heart recipient has extensive damage and has failed medical and/ or surgical treatments, and possibly devices. So another heart that matches size, blood type, etc becomes available and is used as donor to replace the recipient sick heart. Use heart lung machine to support the patient while operation done.

When can a heart transplant be done?

Last resort. Having a heart transplant is usually the last resort -- if a person is not doing well in spite of maximum therapy -- or a younger person with longer lifespan expectancy of he/she gets a heart transplant -.
Several steps. Whenever there is a donor organ available. The recipient will need careful evaluation to determine they are suitable candidates based on the cause of end stage heart disease, their co-morbidities (other diseases), their blood and tissue type, their size (for a particular donor heart) and there ability to care for the heart after it is transplanted.

What is the cost of heart transplant?

Close to 1 million. Depending on the center the cost is close to 1 million dollars in the us. Fortunately most insurances, including medicare and public aid, cover transplants.
Over 100, 000. It is between 100 and 150 thousand. Followed by about 200 dollars per month for drugs.