Heart Failure Support Group
Heart failure is a condition that can result from any structural or functional cardiac disorder that impairs the ability of the heart to fill with or pump a sufficient amount of blood throughout the body. It is often undiagnosed due to a lack of a universally agreed definition and difficulties in diagnosis, particularly when the condition is considered "mild."
how quickly a heart stabilises after a massive shock is difficult to guess with such factors of age, general health needing to be part of this equation, but I think your doctor is watching your progress closely by the sound of it.
http://health.clevelandclinic.org/2013/09/ejection-fraction-and-heart-failure-video/