Activity will include full planning and execution of paid search recommendations, including management of the Google grant aid, provided to charities to help enhance digital advertising strategies.
The British Heart Foundation is looking to digital to help maximise communication with its target audiences, and particularly boost the use of its Google grant aid.
Laila Takeh, online manager at British Heart Foundation, said: "Search has already started to improve how we communicate with the right people, in the right way, at the right time.
"With Agenda21 we're hoping to increase the effectiveness of our search activity and increase our online fundraising to fund our life saving work.
"Making the most of every penny given to us by the public, or organisations like Google, is always at the centre of our thinking."
Agenda21's response to the brief was to ensure efficiencies in search and to be mindful of paid activity without affecting current donation activity online.
Matt Nunney, head of search at Agenda21, said: "The importance of efficiencies in digital marketing have never been more crucial than in the current economic climate.
"Our work for the British Heart Foundation will look to decrease the cost to value ratios of online donations and to help the client to grow e-retail and conversion learnings at the same time."