The heart is surrounded by fibroserous sac, the pericardium. This is composed of two layers and anchors it to the surrounding structures
Great visuals. Coronary artery supply and corresponding MIs | Sketchy Medicine
Coronary Circulation and the 12 Lead EKG
Heart Blood Flow Path | ... blood passes through the heart twice for the body to be supplied once
Looking at the outside of the heart, you can see the heart is made of muscle. The strong muscular walls contract (squeeze), pumping blood to the arteries.
The Quick and Dirty Guide to Cardiology II: Coronary Circulation - MedicTests.com
Anatomy of heart and direction of blood flow