Really only 15-25% liver, the rest is pork, flavoured with garlic and red wine. In Umbria they also make a 'sweet' version, with raisins, pine nuts and orange peel. Similar salami in Tuscany and Emilia are called sambudello.
The Mazzafegato dell'Alta Valle del Tevere, produced along the upper Tiber in Umbria, is in the Slow Food Presidium.
Image by taccuinistorici.it