The heart can enlarge very quickly without any warning of a problem. For a perspective the heart size varies within a normal range to increase cardiac output. A larger left ventricle...more volume and increased contractual strength. This compensation helps the system to maintain a blood flow balance between the right and left side of the heart.
If the underlying cause is not corrected, the heart size will increase to a size where there is an impediment to contractions. The weaker contractions cause an imbalance between the right and left side and blood backs up into the lungs causing congested heart failure (fluids leak into lung tissues).
There is a calculation with a test procedure that relates to the contractual strength and the heart's efficiency. The calculation is referred to as the ejection fraction (EF) and that is the amount of blood pumped out with each heartbeat. Normal is 55-75% and below 29% is considered heart failure (heart is too weak to supply an adequate supply of blood to meet the system's demand). You post indicates about 10 to 15% is pumped out with each stroke. All or almost all of the heart is working (sometimes heart cell damage from a previous heart attack impedes heart wall movement reducing contractions), but enlargement itself can cause a weaker heart and arrhythmia..
The heart quickly enlarges when it is overworked by pumping against the high resistance of constricted blood vessels. Also, the kidneys increase the volume of blood adding to the workload.
Sometimes the workload can be reduced with medications to dilate the vessels and decreasing fluids with a diuretic, and the heart returns to normal size.
my dad also has a pacemaker/delif we have switch drs , and the new dr said that the pacemaker was not big enough and that the company admits putting in the wrong one. I am so confused because we are trying to get information so tha we can understand whats going on. Were wondering if the right one was put in a year ago would this have helped not to damage anymore of his heart. He has been in and out of the hospital for the past year. We are in the hospital right now because his CHF started again. We are waiting on the new pacemaker plus the third lead is not where it should be, so we got to put a new one in. Thank you so much for explaing about the enlarge heart. dailey40