So the warm blood flows

Through the large four-chambered heart

Maintaining the very high metabolism rate they have

Mammal, mammal

The heart is one of many organs inside you that function with great persistence and they all work in tandem to keep you alive--with your flaws and all--to the last breath. As we change, our bodies can and will adapt to keep us alive. The human body is cool. Nothing's perfect, but optimism is nice.