The dispatcher calls our unit to back up medics on a cardiac arrest. The dispatcher says it’s a 3-month-old baby.

“Damn it,” Bronson says. I get nervous and read more on the KDT display. Apparently the baby isn’t moving or crying. Bronson hits the “63” button indicating we’re en route to the assignment, then flies through every intersection while I manipulate the siren. “Jobs involving infants are rarely what the initial assignment is about,” he shouts to me, and himself, as he takes a turn too quickly, sending me into the passenger-side door.

“Probably a seizure,” I agree, righting myself, hoping that’s the case, wishing it.

We turn the corner onto a tree-lined block in Midwood, Brooklyn, with pretty houses. We grab the oxygen bag and the pediatric bag but leave the defibrillator behind, as we are not allowed to defibrillate a child under 1 year of age. An engine company from the Fire Department turns the corner as we rush inside.

We’re met by a young Russian woman who speaks no English. She’s crying, holding a limp baby that looks perfect, like it’s sleeping, like a porcelain doll. The call is legit, and my nervousness immediately turns into fear and adrenaline.

Bronson grabs the child. The baby boy is not breathing and has no pulse. I shout into the radio for an ETA for the medics and we run to the ambulance doing CPR and mouth-to-mouth on the infant.

The medics are three minutes out. The nearest 911 receiving hospital is five minutes away. Bronson throws the ambulance keys to a firefighter and we’re off to the hospital. Now I’m bagging the infant, using the oxygen bag to force air and supplemental oxygen into the baby’s lungs, while Bronson is doing CPR. A police vehicle follows with the baby’s mother.

We’re four blocks from the hospital when the medic bus radios us to stop — they’re right behind us. The firefighter pulls over and both paramedics jump in. They throw Bronson the keys to their ambulance. I wish they’d thrown me the keys, as I don’t want to be back here with this baby.

The medics look at each other as the ambulance gets going again and one simply says to me, “Keep bagging,” while the other takes over CPR. This close to the ER, there’s no point in trying to intubate the child or start an IV in a moving ambulance flying down a busy street, jolting us all around. Better to just get there fast.

Thirty seconds later we run into the ER carrying the child. The doctors take over as the police car arrives with the mother. They do all they can — intubate, push medications, but nothing works. Twenty-five minutes later they call the code.

Several nurses are wiping their eyes. They have children, too. I think of my own children, at home with my mother, and miss them. “Probably SIDS,” the doctor tells me, peeling off his gloves.

Afterwards, Bronson and I park and sit quietly in the ambulance. I break the silence by mentioning a documentary I saw a few nights earlier on cable called “The Boys of Second Street Park,” about a group of Jewish kids growing up on the Brighton Beach basketball courts in the 1950s and ’60s. Some were successful personally and professionally. Some got derailed by drugs. Some just got worn down by life.

I tell Bronson about how two of the men lost young children, one to an unspecified cancer, the other to leukemia. That little boy died in his father’s arms as he was bringing him to the hospital. The father, distraught 20 years after the fact, begged of the interviewer, “Where do you go? What do you do?” He said he continued driving his son to the hospital, holding him up as he slumped. He said he misses his little boy every day, he was a great kid.

We both have sons, so I know this hits home for Bronson as much as it did for me. I finally cry, and he laughs at me — his way of saying, “Losing a child, this just does not compute.”

“The documentary ended,” I say, wiping my eyes, “with the men all laughing, playing basketball on the court they grew up on. But I wanted to see the final scene,” I tell Bronson, “the one never filmed, where the man who got derailed by drugs and divorce and who lost his little boy to cancer gets home to his furnished apartment, makes a sad little dinner, and puts himself to bed. What does he think about as he closes his eyes?”

Bronson has the answer. “Just his little boy,” he says.

Ms. Klopsis is an emergency medical technician on an ambulance in Brooklyn. This column details her observations and experiences. Some names and identifying details have been changed to protect the privacy of patients.