  This paper is twofold. The first part aims to study the long-time asymptotic
behavior of solutions to the heat equation on Riemannian symmetric spaces $G/K$
of noncompact type and of general rank. We show that any solution to the heat
equation with bi-$K$-invariant $L^{1}$ initial data behaves asymptotically as
the mass times the fundamental solution, and provide a counterexample in the
non bi-$K$-invariant case. These answer problems recently raised by J.L.
V\'azquez. In the second part, we investigate the long-time asymptotic behavior
of solutions to the heat equation associated with the so-called distinguished
Laplacian on $G/K$. Interestingly, we observe in this case phenomena which are
similar to the Euclidean setting, namely $L^1$ asymptotic convergence with no
bi-$K$-invariance condition and strong $L^{\infty}$ convergence.
