When operating a light multiengine airplane at VMC, what should the pilot expect regarding performance?

When operating a light multiengine airplane at VMC, the pilot should expect that the heading will be affected significantly. At VMC, which is the minimum control speed, it's the slowest speed at which the airplane can maintain controlled flight with one engine inoperative. At this speed, the airplane is on the edge of control, which means that any deviation from it, including adverse yaw due to asymmetric thrust from the operating engine, can cause the airplane to veer off course, impacting its heading.

The other options involve additional aspects like altitude, climb rates, and cruising speeds that are not directly relevant to the basic understanding of VMC. While altitude may be maintained at VMC, it becomes more critical to focus on maintaining control, especially the heading, since a departure from this can lead to loss of control, rather than just looking at the altitude or climb performance. Therefore, focusing on heading gives the pilot the most critical aspect of control performance under these conditions.