A method to constrain a heart including the steps of: injecting a
biopolymer into a pericardial space of the heart; inducing intramolecular
or intermolecular interactions in the biopolymer in the pericardial space
to modify physical properties of the biopolymer in the pericardial space,
and constraining the heart with the modified biopolymer in the
pericardial space.