An FDNY firefighter has died of a heart attack just months after he was fired as part of the city’s effort to free up funds for its migrant crisis — leaving his grieving widow and kids struggling to keep a roof over their heads.

Derek Floyd, 36, suffered cardiac arrest and passed away April 15, four months after the city gave him the boot as part of a larger effort to pare down staff and pay for housing and services for the tens of thousands of migrants flooding the Big Apple.

Floyd was one of about 10 Fire Department employees who had been on “long term duty” — either injured on the job and given office work or out sick for an extended period — and fired weeks before Christmas, FDNY sources told The Post.

Derek Floyd, 36, left behind a wife, 6-year-old son and 2-year-old daughter.

Floyd, a veteran who served three tours in the Middle East with the Marines, had been among those working a desk job — toiling in the Fire Department chaplain’s office — because he had suffered another heart attack in 2019 while he was in the Fire Academy.

In the chaplain’s office, the firefighter, who was on modified duty, helped arrange the funerals of fallen FDNY members.

The married dad of two young children was trying to become medically cleared to re-enter the fire-fighting force before he was fired.

Floyd had been just shy of vesting additional medical benefits for his family and more than $600,000 worth of death benefits when he was booted, now leaving his family with nothing despite his years of service.

“I wouldn’t wish it on anyone,” Floyd’s 34-year-old widow Cristine told The Post of the family’s experience.

“I think it definitely took a toll once they let him go,” she said of her husband’s firing. “He always tried to, like, stay positive about it, and he wasn’t really angry.

“But you see a person, and the wheels are turning in their brain where they’re just constantly thinking, so I definitely think it did affect us.”

After Floyd was fired, he found a job with a non-profit that helps veterans, but the pay was a fraction of what he made with the FDNY, the benefits were limited, and the hours prevented him from spending time with their kids, a 6-year-old boy and 2-year-old girl.

“He used to be so present for, like, our kids and stuff,” Cristine said. “Being a firefighter was something he was really passionate about. He was really a big-time, like, family person, he was all about his kids.

Floyd died of a heart attack April 15 after serving with the FDNY since 2019.“If Derek would have stayed on, he would have had a life insurance policy with the FDNY,” the widow said. “That would have helped out financially because right now, it’s really bad. I’m honestly swimming in a lot of debt.”

Floyd’s firing was part of City Hall’s plan to slash the FDNY budget by $74 million by the end of 2025 to make way for migrant spending.

It is unclear how many “long-term duty” staff will ultimately be let go as part of the effort, but there are typically between 800 to 1,000 designated individuals at any given time.

Also facing cuts is the NYPD, which is to have its budget slashed by $132 million through the axing of five upcoming Police Academy classes.

The city Department of Education will lose about $547 million, too, and the Department of Sanitation will have its budget cut by $32 million.

The firefighter did three tours of duty in the Middle East while he was with the Marines before joining the FDNY.Floyd’s firing — and the circumstances that have now befallen his family since his death because of it — have left some outraged.

“What disturbs me the most is that the FDNY is understaffed by hundreds of firefighters. Terminating [Floyd] was absolutely unnecessary,” Uniformed Firefighter Association President Andrew Ansbro told The Post.

“He had an important job, and the FDNY actually needed him in that unit. He was terminated so the department could prove that they were making cuts. He deserved better,” Ansbro added.

Cristine said that watching her husband struggle to make ends meet while being present with his family after the firing was the worst part of everything they’ve experienced.

“I really, really loved him, and so it was hard,” she said.

“We are heartbroken over the passing of former Probationary Firefighter Derek Floyd, and will explore all financial, legal and legislative options to help his family and ensure they have the support they need during this time,” said Fire Commissioner Laura Kavanagh.

City Hall did not respond to The Post for comment

Donations to help the Floyds can be made out to the “New York Firefighters Foundation” and sent by mail addressed to FF Derek Floyd C/O UFA – NYFFinc 204 E. 23rd St, NY,NY 10010.