Which of the following is triangular in shape?

The pancreas is the organ that is typically described as triangular in shape. It is located in the abdomen behind the stomach and extends horizontally across the posterior abdominal wall. Its shape resembles a triangular prism, particularly when viewed from the side, with a broader head that tapers off toward the tail.

Regarding the other options, while the liver is a large organ and has a somewhat irregular shape, it is not triangular. The heart, though it has a somewhat conical form, is more rounded rather than triangular. The bladder is generally more oval or balloon-like in its appearance, not fitting the triangular description at all. Therefore, the pancreas is the primary structure that aligns with the description of being triangular in shape.