What happens in the heart of chf patients?

See Below: Increased pressure and/or increased volume leading to a dilated or thickened heart. This is a gradual process which is why early detection and intervention (diagnosis and medication) can make a significant difference.

Muscle weakness: It's a reduce efficiency of the myocardium. The pump function to supply oxygenated blood to the body do not work well. Due to direct damage to the heart or overloading. Can be classify as systolic vs dyastolic chf, depending on the status if the heart muscle and the etiology. Example: systolic CHF due to chronic ischemic heart disease vs dyastolic CHF due to hypertrophic cardiomyopathy.