Because of the long-term nature of life insurance policies including interest rate guarantees and the current low interest rate environment, the fair valuation of insurance contracts is of particular interest. Fair valuation is often discussed on a single contract basis or from the viewpoint of a homogenous portfolio, i.e. a portfolio with identical policies. However, insurance portfolios are heterogeneous, i.e. consist of many different contracts. These contracts interact, e.g. because they share reserves, profits and the risk of default of the insurance company. In this presentation, we introduce a methodology how interactions within heterogeneous insurance portfolios can be measured and provide some sample analyses dealing with the question “what are the effects of a differentiation of surplus participation on existing policyholders, new policyholders and the shareholders?”.