Please Explain Exactly What Congestive Heart Failure Is. My Wife

Please explain exactly what congestive heart failure is. My wife has asked me and I feel I haven't given an adequate explanation. I've had two heart attacks, triple by-pass, had my heart shocked twice, had cardiac ablation and will receive a pacemaker on the 28th. Please use the KISS approach when you answer my request. Louis Sassman, 78 year old male, Corpus Christi, Texas.