"In the heart of the Sun" - within 17 minutes of arc of the Sun's Ecliptic position and therefore corporally joined to the body of the Sun. The sun's radius on the Celestial Sphere was considered to be 17 minutes of arc. Traditionally a Cazimi planet is fortified.
"is when a Planet is in the heart of the Sun; that is, not distant from him above 17 min. as Mars in 10 deg. 30 min. of Aries, the Sun in 10 deg. 15 min. of Aries; here Mars is in Cazimi." [PA
A planet within 17 minutes of the Sun, by conjunction, is said to be cazimi, and at the "heart of the Sun". This greatly strengthens the planet. It can be likened to a man who has been raised up to sit beside the king.
also casimi From the Arabic center of the solar disc. A planet that forms a conjunction with the Sun within 30' of partile is said to be cazimi, literally "burnt up" by the Sun. The Sun, representing the ego, engulfs the energies of a cazimi planet.
A planet within 17 minutes of arc of the Sun's ecliptic position, the "heart of the Sun", is fortified by Cazimi. See Combust.
Cazimi (also spelled Casimi, and sometimes called Zaminium) is a technical Arabic word meaning "heart of the Sun" or "in the heart of the Sun." It is an astrological/astronomical term meaning a planet that is in exact conjunction with or very near the precise center of the solar disc. A planet that forms a conjunction with the Sun within 17' (arc minutes) of partile (exactitude) is said to be Cazimi, literally engulfed and fortified by Sol and, as it also may be interpreted, "in the heart of the Sun."