Terms weren't disclosed. IHeartMedia already holds a minority position in Voxnest.
Voxnest, founded in 2018 and headquartered in New York, provides tools to create and distribute podcasts as well as to measure results and draw advertising.
IHeartMedia, New York, says it's the world's largest publisher of podcasts.
Bringing in Voxnest, the company's chairman and chief executive, Bob Pittman, said in a statement, will enable it to earn more from its podcasts and will benefit other podcast publishers "that are part of the Voxnest network and the advertisers who are using it."
The Voxnest network includes more than 10,000 podcast publishers, iHeartMedia said.
"The podcast marketplace has been fragmented, with supply and demand spread across multiple platforms -- creating scale challenges for marketers who want to buy podcasts,” said Francesco Baschieri, CEO of Voxnest.
And he said "podcast creators and networks have not had an effective way to fully monetize their content and brands.
"With this combination, ... one podcast technology platform [can] bring together all of the demand sources with the largest supplier of podcast inventory."
Baschieri said the podcast industry has grown rapidly, with "more than 100 million Americans listening to a podcast every month."
Podcast publishers will be able to use Voxnest’s advertising technology to target the right listeners based on demographics, devices, and interests. They could also make use of the dynamic ad insertion and full podcast analytics platform, provided by Voxnest.
IHeartMedia operates 850 radio stations in the U.S. And with more than 251 million downloads each month, iHeartRadio says it's the leading commercial podcast publisher, according to Podtrac. The iHeartPodcast Network offers more than 750 original podcasts.