This result states energy dissipation identity for harmonic map heat flow: given (M,g) be a closed smooth Riemannian manifold, let (N,h) be a smooth Riemannian manifold, and let u: M [0,T) N be a smooth solution of the harmonic map heat flow t u = g(u),.... It is useful in harmonic map theory and elliptic regularity, where variational identities, curvature estimates, and compactness arguments control geometric objects.