Julio Gonzalez, a jilted lover whose arson revenge at the unlicensed Happy Land nightclub in the Bronx in 1990 claimed 87 lives, making him the nation’s worst single mass murderer at the time, died on Tuesday at a hospital in Plattsburgh, N.Y., where he had been taken from prison. He was 61.

The cause was apparently a heart attack, prison officials said.

Mr. Gonzalez had been at the Clinton Correctional Facility in Dannemora, N.Y., where he was serving 87 concurrent sentences of 25 years to life in prison after being convicted of starting the fire, which swept through the club early on March 25, 1990, a Sunday.

At the time, the club, on the second floor of a run-down building on Southern Boulevard in the East Tremont neighborhood, was crowded, mostly with Honduran immigrants celebrating Carnival. Only six people escaped.

Happy Land was found to have lacked fire exits, alarms and sprinklers. It had been ordered closed in November 1988, and its operators were facing eviction.