Abstract The American Post Keynesians – those who attach importance to the capital ‘P’ and the absence of a hyphen between ‘post’ and ‘Keynesian’– claim to be Keynes' most literal interpreters or the ‘truest’ Keynesians (Holt et al. 1998: 17). This paper compares the Post Keynesian interpretation of the Principle of Effective Demand, i.e. the D/Z-model, with Keynes' own presentation in chapter 3 of the General Theory– and finds substantial differences. A re-interpretation of the D/Z-model is offered that would bring it into line with chapter 3.