Delivery of therapeutics directly to the heart remains challenging. According to a new study, the modification of proteins with tannic acid (TA) can improve their ability to target specifically cardiac tissue, because of the affinity of TA for macromolecules such as collagen and elastin, which are abundant in heart tissues. TA-modified (TANNylated) green fluorescent proteins (GFPs) intravenously injected in mice were detected mainly in the heart after 6 h, whereas un-TANNylated GFPs accumulated in the liver. Injection of TANNylated fibroblast growth factor (FGF) in mice after myocardial infarction reduced the infarct size to 16.3% of the whole heart size compared with a 50.5% infarct size with no treatment and 30.5% with un-TANNylated FGF treatment. TANNylated FGF also improved cardiac function, validating the therapeutic potential of TANNylated-based strategies for heart diseases.