Many lines of evidence have established that MMPs harboring gelatinase activity, such as MMP-2 and MMP-9, facilitate the progression of VO-induced HF by degrading extracellular matrix.[26–30] As such, we examined MMP gelatinase activity in left ventricle by in situ zymography in both TFAM and Twinkle mice. The gene discussed is MMP9; the disease is hydrops fetalis.