Final answer:
The pericardium is the correct answer, as it is the saclike membrane surrounding the heart and consists of the fibrous pericardium and serous pericardium.
Step-by-step explanation:
The pericardium is the saclike membrane surrounding the heart, segregating it from other mediastinal structures. It is composed of two distinct sublayers: the fibrous pericardium, which provides protection and structural support, ensuring the heart maintains its position in the thorax; and the serous pericardium, which includes the parietal pericardium fused to the fibrous layer as well as the visceral pericardium or epicardium directly fused to the heart. The pericardial cavity, containing lubricating serous fluid, lies between the serous layers reducing friction during the heart's activity.
Therefore, the correct answer to the question "The ______________ is the saclike membrane surrounding the heart?" with options A) endocardium B) bundle of His C) pericardium D) sinoatrial node, is C) pericardium.