In classical economic theory (as formulated by Quesnay, Smith, Ricardo and Marx), the economic activity is described as a circular process that involves the transformation of money to commodities and of commodities to money. The process is a qualitative and quantitative depiction of the turnover of capital from the sphere of production to the spheres of exchange and distribution, where it assumes different forms, namely, the productive capital, the commercial capital and the money capital, respectively. This process is known as the Circuit of Capital and, for many economists, was the prime tool to analyse the process of labour, the reproduction and accumulation of capital and the possibility and actuality of crises in the capitalist mode of production. In a paper in 1982 and two books in 1986, Foley formulated a mathematical model for the circuit of capital using integral equations. In the present work, we reformulate this model into a closed and autonomous dynamical system. Not surprisingly, this model resembles the famous epidemiological models, used to describe a similar circular process for the spread of a disease: the money capital resembling the ‘susceptible’, the productive capital resembling the ‘infected’ and the commercial capital resembling the ‘removed’. The equilibrium points of the system reveal the cases for a ‘normal’ phase of expansion, as well as for an ‘excess capital’, an ‘excess commodities’ and an ‘excess money’ crisis, all of which are associated with a specific type of stagnation in the economic literature. However, the stability of each indicates the existence of (at least) one limit cycle, separating the short-run stable phase of ‘normal expansion’ from the long-run unstable phase of a crisis.