Visual modeling languages propose specialized diagrams to represent behaviour and concepts necessary to specify IT systems. As a result, to understand a specification, the modeller needs to analyze these two types of diagrams and, often, additional statements that make explicit the relationships between them. In this paper, we define a visual contract notation that integrates behaviour and concepts. Thanks to this notation, the modeler can specify, within one diagram, an action and its effects on the specified IT system. The notation semantics is illustrated by a mapping to Alloy, a light weight formalization language.