Heth is the eighth letter of the Syriac abjad, with the numeral value eight. It writes a voiceless pharyngeal fricative, a sound made by narrowing the throat well behind the place of an ordinary h, and it is one of the two pharyngeals that Syriac keeps from its Semitic inheritance. The other is the sixteenth letter, recorded in the modern character standard simply as E.
Heth joins on both sides and takes the full set of positional shapes, so it carries a connected run onward rather than breaking it. Its name is the inherited Northwest Semitic word for a fence or an enclosure, the same noun behind Hebrew cheth.
The sound is the interesting part. Pharyngeals are among the most distinctive features of the Semitic languages and among the first to weaken when a language changes or when its speakers shift to another. In the modern spoken descendants of Syriac the pharyngeal has weakened in many dialects, and heth is read in ways that would not have been recognised as distinct in the classical language. The letter is still written, and in the liturgical reading of classical Syriac it is still kept apart from he.
That gap between what is written and what is said is not a fault in the script. It is what happens when an alphabet outlives the pronunciation it was fitted to, and it is the ordinary condition of any liturgical language still in daily use.