Noted for his large assortment of off-speed pitches, Pena was a standout in the minors (146-85). He was used regularly as a major league starter only by the A’s, for whom he lost a league-high 20 games in 1963. He teamed in Kansas City’s rotation, and later in the St. Louis bullpen, with fellow Cuban Diego Segui. After a poor year in Triple-A ball in 1969, he was signed by the Royals in 1970 as a batting practice pitcher, and was impressive enough that the Pirates signed him that June. His 22-3 (1.25) record in two minor leagues in 1972 earned him three final ML seasons. He later scouted for the Tigers.