The LIFE Green Heart project contributes to create a new green lung in the city of Toulouse, and to study the effects of revegetation in cities. It will generate 10 hectares of green spaces, among which 2500 trees planted, with the objective of mitigating the urban heat island effect by -3°C during heat waves. So far, 1.5M€ have been invested and 2.3M€ more are expected.