The trustless nature of smart contracts and blockchains make them interesting for use between organizations, where the participants do not want to blindly trust each others. Often such processes between organizations need to be implemented as business transactions. The rapid development in blockchain technology has lead to a big variety of different blockchains, with different properties and feature sets. If two businesses that use different blockchains want to interact with each other, this leads to business transactions, involving smart contract invocation over different blockchains. The transaction semantics of such cross chain smart contract invocations are unclear. In this thesis we present an adjusted saga pattern as transaction model for cross chain smart contract invocations. We further present a BPMN extension that allows us to utilize the capabilities of existing process engines for the saga pattern, and allows for integration of cross chain smart contract invocations in existing processes.