The only tear of heart muscle I have heard about is a papillary muscle tear or the doctor may be referring to a ruptured aneurysm. With either situation, it seems you would have been told because that is serious.
For some insight, the papillary musce is where the heart valves are tethered with chords tindae. The condition is of interest to me because I had an enlarged left ventricle years ago and now have mitral valve regurgitation. When the left ventricle enlarges that stresses the chords (stretches, elongates), and it may not be able to completely close the valve opening with the result of blood backflow. Sometimes the chord tindae may tear away from the papillary.
"During a heart attack, the spasms of the heart may cause the papillary muscles to tear. Since the papillary muscles attach directly to the heart valve, this often causes the heart valve to tear as well".
Would need more information about a "tear" such as the location, symtoms, what tests, etc.to evaluate for seriousness, treatment and provide a meaning.
Thanks for the question, and sorry to hear of your mother's condition. If you have any follow-up questions, you are welcome to respond. Take care.