Once I get that call, everything changes. I might be out with my children, at the movies with my wife, or perhaps sleeping when the call comes: There is a donor for one of our patients on the pediatric cardiac transplant waiting list.

After that, it is hard to think about anything else. Once we accept a heart for transplant, a cascade of events unfolds that will change the lives of many people. Even if I don’t need to be at the hospital for a few hours, mentally I am already there. In my head I am working over the details of the operation, reviewing what our cardiologists think of the donor and evaluating the stability of the recipient.

Heart transplants almost always occur at night. Because hospitals are not reimbursed for organ harvests, operations to remove the donated organ are typically placed at the end of an operating room’s elective schedule, late in the day. The donated organ, which may be hundreds of miles away, must be brought to our medical center. We usually don’t get to start the implant of the donor heart till sometime after midnight.

Coordination and timing of a heart transplant could become an Olympic event, involving at least two teams at two hospitals – a harvest team and a donor team — each with a different set of objectives. I will make at least 10 calls before I get to the hospital. Dozens of people on our transplant team will be alerted: cardiologists, nurses, anesthesiologists, surgeons, intensivists, perfusionists. As is customary, we send our own team of surgeons to pick up the heart. Other transplant teams may also be involved, sending their own sleep-deprived surgeons in to harvest the lungs, liver or kidney.

The donor story is always horrible. The children frequently succumb to trauma, terminal illness or, perhaps most tragic of all, child abuse. The donor stories stay with me, and lately I have stopped asking how the child died. I cannot forget the father who, backing out of his driveway, accidentally ran over his child. My children still don’t understand why, whenever they are playing basketball in our driveway, I make them stop and line up where I can see them before I pull my car out.

Every harvest surgeon arrives at the donor hospital with an ice-filled cooler, often having traveled late into the night via some combination of plane or helicopter or ambulance. The organ harvest is as critical as the transplant itself. If an organ is not protected and preserved well, the transplant won’t work, no matter how technically perfect the transplant operation might be. Travel time needs to be as short as possible; every hour between harvest and transplant can have deleterious effects on organ function.

The schedule for the transplant operation itself is made, adjusted, then readjusted. We all know that it’s only a guideline and that delays are the rule. Eventually it all starts to come together.The heart is placed in a cooler. The donor surgeon rolls it through the hall, with one hand on the cooler and one hand holding his phone to his ear, walking to the ambulance that will take him to the airport. He tells me that they are on their way and that the retrieval went fine. “No issues,” he says. I always reply the same way, though I’m not sure why: “Safe travels,” and “Bring me back a winner.”

Back at our operating room, the pediatric cardiac anesthesiologists have been kept apprised of how things are progressing. We need to have our patient completely ready to implant the heart as soon as it arrives. The family hugs the child on his way to surgery, with kisses and tears all around. The patient has been partly sedated already and remains the calmest of everyone. The parents ask for “some of what he is having.” We smile and say that we are not allowed.

We will make the first incision just before midnight so that we are ready to implant the heart when the donor team arrives. The donor team people arrive five minutes later than expected, at 1 a.m.; in New York City there is traffic even at this hour. They join us just as we are removing the recipient’s own heart.

As the donor surgeon scrubs in to join me for the implant, he tells me they used the ambulance sirens to get through the traffic. Once the diseased heart is out, we can see that it is three times the size of the new heart. For technical reasons, this is good. The new heart will fit easily in the chest.

The implantation proceeds without incident. There are certainly more difficult procedures in congenital cardiac surgery to perform than a heart transplant, but few freighted with more anticipation. After all, the heart that we are asking to sustain our patient started off this morning in another child. The transplant cardiologist who has been taking care of this child for the last year meets us in the O.R. at 4:15 a.m. “How is it going?” she asks.After the heart is sewn in and we allow it to be perfused with blood, it starts to beat. Within 30 minutes, it is beating strongly enough that the patient can come off the heart-lung machine. The boy is on his own.

Another cardiologist, an expert in echocardiography, has joined us and tells us that the new heart is working well. The patient’s cardiac function is the best it has been in over a year. We can begin to close.The next conversation I have will be with the family. The sun is starting to come up, and it is a new day.