As one enters this chapel, one might be struck by how it's features makes it appears more akin to a full fledged church than to what most of us would think of as a chapel. In point of fact this was at one time the original (albeit rebuilt) church of San Zaccaria. Various reconstructions and interventions have happened for various reasons to over the years, but this particular space was left relatively untouched, becoming a chapel in what is now the much larger and more Renaissance art oriented church of San Zaccaria.
This particular altarpiece is the work of the woodcarver Ludovico da Forlì and the artists Antonio Vivarini and Giovanni d'Alemagna, completed circa 1444. Some of painted panels in this piece are older however and not original to the piece, specifically those of the Virgin and Child, and the figures of St. Blaise and St. Martin to either side. These were done by Stefano di Sant'Agnese in 1385 and originally they formed a part of another altarpiece. These were not put into place in the present altarpiece until in the mid nineteenth century, though stylistically, they mesh quite well.
To either side of these three central panels are the figures of St. Mark and St. Elizabeth. These are, by comparison, original to the altarpiece.
This particular altar recently underwent a long period of restoration works, only recently completed and those interested can read more about that by way of Finestre sull'Arte.
It is an incredibly beautiful and impressive altarpiece in what is one of the most important liturgical spaces in all of Venice.