What physical change defines dilated cardiomyopathy (DCM) when it affects the Great Dane heart?

heart muscle becomes thin, weak, and enlarged

Dilated cardiomyopathy (DCM) is a serious form of heart disease frequently seen in this massive breed. This condition involves a progressive structural deterioration within the heart muscle itself. Specifically, the cardiac muscle tissue weakens, thins out, and causes the chambers of the heart to enlarge abnormally. This pathological remodeling severely compromises the heart's contractile ability, meaning it cannot efficiently pump the necessary volume of blood throughout the dog's system. As the disease advances, overt signs such as chronic weakness, pronounced fatigue, and visible labored breathing manifest, although the onset can sometimes be subtle initially.