Sam is an economics teacher who wears wire-rimmed glasses and his Adam Smith tie on the first day of classes. He is “tall and lanky” (2), is 30 years old, and has a significant amount of education and teaching experience. Sam is the main protagonist of the novel, and his understanding of economics drives the primary plot. It is Sam who uses the titular phrase “the invisible heart” to describe the innate compassion he sees as a fundamental part of capitalism. Initially he appears unflappable in his debates with Laura. Even when she accuses him of having “evil” and “satanic” worldviews, he laughs it off and takes no offense.

However, it is Laura’s brother Andrew’s accusation of heartlessness that results in him having to leave the dinner party. Sam has spent most of his 30 years refusing to modify his views for the comfort of others. He cares deeply about his beliefs and is willing to expose them to scrutiny; in fact, he insists on it. Laura has such an intense effect on him, though, that for a moment, he pretends to be able to swim with the current. Over the course of the novel, his initial appearance as calm and collected is slowly revealed to be far more complex.