A name's Heart Number (also called the Heart's Desire or Soul Urge number) is calculated from the vowels only. Where the Personality Number describes how a person appears to others, the Heart Number describes what actually motivates them underneath: the private wants and values that drive their choices even when no one else can see them. Vowels are considered the "soul" of a name in Pythagorean numerology, carried through in speech even when consonants are dropped or mumbled.

A Heart Number of 33, a master number, points to an inner drive to nurture and uplift on a wide scale. Underneath whatever this person shows the world, what they privately want most is to care for others as a calling rather than an obligation, the rarest and most selfless of the heart numbers.