Returning to baseball in early 1945, Hetki made his major league debut with the Reds in September of that year. He went 1–2 with a 3.58 ERA in two starts and three relief appearances. His most productive season came in 1946, when he finished 6–6 with a 2.99 ERA in 32 games, including 11 starts and four complete games. Hetki was with the Reds through the 1950 season, spending part of this time in the minor leagues. As a result, in 1949 he went 16–14 for the Syracuse Chiefs of the International League, ending fifth in the league in wins and second in innings behind Al Widmar. He then was purchased by the St. Louis Browns from Cincinnati in October 1950. Hetki spent 1951 with the Toronto Maple Leafs, and this time he led the International League with 19 victories and 256 innings pitched, while tying for second in ERA with Karl Drews behind Jackie Collum. He was called up by the Browns in 1952 and appeared in only three outings for St. Louis, going 0–1. After that, he was selected by the Pittsburgh Pirates from the Browns in the 1952 Rule V Draft. Working mostly out of the bullpen, Hetki won 3 and lost 6 for the Pirates in 1953 and went 4–4 in 1954, leading the National League in games finished in that last season. Overall, Hetki posted an 18–26 record with a 4.39 ERA and 13 saves in 214 pitching appearances, striking out 175 batters while walking 185 in 525 innings of work. Additionally, he went 101–71 with an ERA of 3.27 in eight Minor League seasons between 1942 and 1956.
Winter league career
In between, Hetki played winter ball from 1951–52 with the Navegantes del Magallanes club of the Venezuelan Professional Baseball League, collecting an 18–12 record with a 3.26 ERA in 52 games during the two seasons. On February 14, 1952, Hetki made history during the longest game played in Winter League history, as Magallanes and Cervecería Caracas battled to a 3–3, 18–inning tie game which lasted three hours and ten minutes. Hetki hurled all 18 innings for Magallanes, setting a record for a pitcher that still stands. Hetki later pitched two complete games for the VPBL champion Magallanes in the 1952 Caribbean Series, including an 11-inning, 2–1 victory against Panama's champion Carta Vieja Yankees.
Later years
After baseball, Hetki worked for several years as a traffic foreman for Simpkins Industries in Cleveland, Ohio. He moved to Parma, Ohio, after retiring. He died on January 10, 2019.