Tetrodotoxin B

Tetrodotoxine B is a drug made by Bruce Banner to slow down his own heart rate to keep him from transforming into the Hulk.

History
Before the S.H.I.E.L.D. Civil War in 2014, Bruce Banner made Tetrodotoxine B to lower his heart rate in order to keep from transforming into the Hulk. Later on the drug was used to help Nick Fury fake his death to stay under HYDRA's radar.