ITD-1 potently blocks phosphorylation of the effector SMAD2/3 proteins induced by TGFβ2, and only minimally in response to Activin A. HEK293T cells are transfected with a Smad4 response element driving luciferase (SBE4-Luc) to test whether ITD-1 blocks Activin A/Nodal and/or TGFβ signaling, which utilize the same intracellular signaling cascade through Smad4. ITD-1 strongly inhibits TGFβ2 signaling with similar efficacy (92% vs. 99% respectively), but with lower potency compared to SB-431542, an ACVR1B/TGFBR1 kinase inhibitor (IC ₅₀ = 850nM vs. 70nM respectively), and is a weak and partial inhibitor of Activin A signals. ITD-1 selectively enhances the differentiation of uncommitted mesoderm to cardiomyocytes, but not to vascular smooth muscle and endothelial cells. ITD-1 reveals an unexpected role for TGFβ signaling in controlling cardiomyocyte differentiation from multipotent cardiovascular precursors .