Chrysalis director of corporate comms Harriet Finney confirmed that the group had brought in Financial Dynamics last week, several weeks after the agency approached her.
The appointment had been made, she said, in a move to make its communications more proactive following 'a couple of difficult messages'.
Chrysalis, which also has music and book publishing businesses, is keen to step up its financial comms efforts following a year in which its share price has underperformed the sector index by around 24 per cent.
In the fourth quarter of last year, Heart 106.2 lost its place as London's second most popular commercial radio station to Emap's Magic 105.4, according to data from Radio Joint Audience Research (Rajar).
Heart took a 5.3 per cent market share compared with Magic's 6.1 per cent. Capital Radio 95.8FM is still London's most popular commercial station with 6.2 per cent.
Last month Heart hired TV and radio celebrity Jamie Theakston to present its breakfast show in a bid to claw back listeners.
FD London chief operating officer Tim Spratt and partner Charlie Palmer are leading the account.