Pedro Feliciano, a relief pitcher who was the workhorse of the Mets’ bullpen for five years — including three straight seasons in which he led the major leagues in appearances, earning him the nickname Perpetual Pedro — died on Monday at his home in Puerto Rico. He was 45.

The Mets announced his death. No cause was given, but Feliciano had learned in 2013 that he had a rare genetic heart condition.

Feliciano, a left-hander, joined the Mets after seven years in the minor leagues and went on to spend his entire nine-year major league career with them. He won 22 games, lost 21 and had a 3.33 earned run average in a career that stretched from 2002 to 2013. He pitched a total of 484 games, the second most in Mets history after the 695 appearances by the All-Star reliever John Franco.

Feliciano was used primarily against left-handed hitters and held them to a .211 average, but he was not just a left-handed specialist. “When you talk about relievers in baseball, in my mind, he’s at the top because he can get out both lefties and righties,” the Mets’ general manager, Omar Minaya, said in 2007.

Feliciano led the majors in games pitched with 86 in 2008, 88 in 2009 and 92 in 2010 — a single-season total that had previously been exceeded only three times in major league history. From 2006 to 2010, he appeared in 408 games and had a 3.09 E.R.A.

His best season was 2006, when the Mets finished first in the National League East: He posted a 7-2 record and a 2.09 earned run average in 64 games.

“I never had to look down to the bullpen to see if Pedro was ready,” Willie Randolph, who managed the Mets from 2005 to 2008, said in a statement. “He was always on call and never said no. I know some days he was tired, but he always took the ball.”

Feliciano left the Mets after going 3-6 with a 3.30 E.R.A. in 2010 and signed a two-year, $8 million contract with the Yankees. But he developed shoulder problems during spring training and was shut down for the season. He had rotator cuff surgery that September and missed the entire next major league season as well.

The Yankees’ general manager, Brian Cashman, blamed the Mets for Feliciano’s injury, saying that they had “abused” him by asking him to pitch too many innings. Told of his comments, the Mets’ pitching coach, Dan Warthen, responded, “They didn’t know that when they signed him?”

Feliciano, Warthen said, “volunteered for the baseball every day” and “wanted to pitch more than we even pitched him.”

After returning to the Mets in 2013, Feliciano announced in spring training that doctors had found a small hole in the exterior of his heart. The diagnosis was left ventricular noncompaction, a condition caused by the failure of myocardial development from birth. When he began pitching in exhibition games that spring, he wore a heart monitor.

He finished the 2013 season, his last in the majors, with a record of 0-2 and a 3.97 E.R.A. in 25 games.

Pedro Juan Feliciano Molina was born on Aug. 25, 1976, in Rio Piedras, P.R. He was picked in the 31st round of the 1995 draft by the Los Angeles Dodgers and later pitched in the minor leagues for the Dodgers and the Cincinnati Reds. The Reds traded him to the Mets in August 2002, and he made his major league debut the next month.

Feliciano left the Mets to play in Japan in 2005 but rejoined the team the next season.

Information on survivors was not immediately available.

The Associated Press contributed reporting.