Human heart. Illustration of the inside of the right ventricle of the heart. The heart contains four muscular chambers, 2 atria, and 2 ventricles which pump blood around the body. During a heart- beat blood flows into the ventricles from the atria. The ventricles contract forcing blood into the arteries because of the closure of valves bet- ween the atria & the ventricles. The white fibrous regions seen here are the chordae tendineae which attach the papillary muscles (centre) to the tricuspid valve above. They maintain closure of the tricuspid valve, allowing the right ventricle to pump blood into the pulmonary artery to the lungs, rather than back into the right atrium.