2014–2019

Heo declared for the 2014 KBL rookie draft and it was widely predicted that he would be picked by Jeonju KCC Egis, which was then coached by his father Hur Jae. Jeonju KCC Egis had been assigned the fourth pick but Hur Jae chose Kim Ji-hoo from Korea University instead to prevent his son's career from being overshadowed. Heo was instead picked by Wonju DB Promy at fifth. He made his debut in October against Goyang Orions, contributing 5 points, 3 assists and 2 interceptions.^[9] Initially the back-up to the backcourt pair of Park Byung-woo and Doo Kyung-min, Heo was gradually given more playing time due to Park's injury problems and poor form.^[10][11] With Park enlisting at the end of the season, Heo was expected to step in as the main shooting guard for the upcoming 2015–16 season. Despite being only in his second season as a professional, he topped the All-Star fan vote.^[12] By the end of the season, he had established himself in the team and won the Most Improved Player Award, having averaged 12.03 points and playing in all 54 league games.^[13][14]

In May 2017, Heo enlisted for mandatory military service and was assigned to the Sangmu team after completing basic training.^[15] He was discharged in January 2019 and immediately returned to DB Promy's roster for the last few rounds of the 2018-19 season.^[16] By then his younger brother turned professional and DB Promy's match-up with his brother's team Busan KT Sonicboom in February drew much attention as it was the first time they had played against one another in the KBL.^[17]

2019–2022

Heo was plagued by persistent back and ankle problems during the 2019-20 season but averaged a career-high of 13.7 points in 14 games and ranked second for 3-point shots among domestic-born players.^[18] With the signing of free agent Kim Jong-kyu, he formed an offensive triumvirate together with Kim and Doo as DB finished the season at the top of the league table; due to the COVID-19 pandemic, the playoffs were canceled and the season's results were forfeited.^[19] He underwent surgery on his ankle at the end of the season, which had been cut short due to the COVID-19 pandemic.^[20] After spending the off-season in rehabilitation, he returned in time for the 2020-21 season.^[21]

Several games into the 2020-21 season, Heo suffered a knee injury. Due to injury problems ravaging the team throughout the season, the players had little time to gel and Heo occasionally had to play despite not being in peak physical condition. DB finished the season at 9th place, second from the bottom of the league table.^[22]

The 2021-22 season began well for Heo as he put up 26 points and 5 rebounds against Suwon KT Sonicboom in the season opening game.^[23] With the departure of Doo, who was traded to Daegu KOGAS Pegasus, he was forced to fill Doo's void as the team's main three-pointer specialist.^[24] However, in October against Goyang Orion Orions, he failed to score ten three-point shots in a row, leading commentators to humorously draw parallels with his father setting the same unwanted personal record during the 2000-01 season.^[25] In December, Heo reached two personal career benchmarks: the most points scored in a single game and reaching 3,000 points. He scored 39 points in DB's narrow loss to Changwon LG Sakers on December 1.^[26] Two weeks later, against Daegu KOGAS Pegasus, he became the 97th player in KBL history to reach 3,000 career points.^[27] He became the first domestic player since the 2011–12 season to score more than 900 points in the regular season, a rare feat for a shooting guard in a league which is still largely dependent on foreign players (mainly forwards and centers) to score.^[28] DB failed to qualify for the playoffs but he was voted into the KBL Best 5 for the first time and was the player from the lowest-ranked team to be selected.