1. This is the heart muscle cardium.: Answer Myocardium 2. This is the fibrous covering of the heart cardium.: Answer Pericardium 3. This is lines the inside of the heart cardium: Answer Endocardium 4. These two chambers of the heart have thin walls, no pumping action, and serve as receptacles for blood from the circulation and lungs.: Answer Right and left atria 5. These two chambers of the heart have thick muscular walls and pump blood to the pulmonary and systemic circulation.: Answer Right and Left ventricles 6. The right atria receives oxygenated or unoxygenated blood from the .: Answer unoxygenated blood from the circulation 7. The left atria receives oxygenated or unoxygenated blood from the .: Answer oxygenated blood from the lungs