2:15 p.m. Possible cardiac arrest.

2484 Arthur Avenue, the Bronx

Capt. Mark A. Bonilla gets the call. He flips on the lights and siren of his red Emergency Medical Service vehicle and steps on the gas. A life in the balance. Adrenaline.

A woman pushing a baby stroller steps into the intersection, head down, and as Captain Bonilla slows down and swerves, she never looks up. Cars dawdle in front of him; some cut him off. This is New York City. People have places to be.

Death and traffic. For the last 23 years, Captain Bonilla has been locked in a perpetual struggle with both, first as an emergency medical technician, now as a paramedic with the Fire Department’s Emergency Medical Service. In that time he has learned a lot about the fickle nature of mortality. He recalls tending to a 107-year-old woman whose heart refused to quit and a young man whose heart never even put up a fight.

On March 16, a longtime colleague and friend, Yadira Arroyo, was killed when a 25-year-old gang member commandeered her ambulance and crushed her beneath its wheels.