Guante won a silver medal for the Dominican Republic at the 1979 Pan American Games and was signed as an amateur free agent by the Pittsburgh Pirates the same year. He was called up to the big leagues in 1982. He played five seasons for the Pirates, working exclusively as a relief pitcher. His strongest season was in 1985, when Guante posted a 4–6 record in 63 games. He pitched 109.0 innings, had 92 strikeouts, a 2.72 ERA and a 1.138 WHIP.