Direct costing is a specialized form of cost analysis well suited for medical areas with DRG-orientated flat rate payments. By comparing case-related variable costs and payments, it is possible to compare the economic benefits of different medical treatments. This aim was pursued by developing a direct costing concept and by its application to invasively and non-invasively treated cardiac patients. The entire database comprised 7 330 cases of a tertiary cardiac center between 2007 and 2011. It was derived from databases of the hospital information system, the materials management department and the catheter laboratory. On the revenue side, DRG payments were included. Costs related to heart catheterization such as material, personnel and maintenance expenses were considered to be variable costs. Contribution margins and relative contribution margins were calculated by introducing the length of hospital stay as a time reference. During the observation period, caseload and annual revenues increased by about 20 percent. Contribution margins were higher in invasively than in non-invasively treated patients (2 097±1 590 vs. 1 614±1 105 €; p<0,001). However, the relative relation of both patient groups was not altered during the observation period. A remarkable shortening of the duration of catheter laboratory examinations was observed between 2007 and 2011 (46,2±39,1 auf 36,7±33,5 min; p<0,001). In the same period, relative contribution margins increased from 461±306 to 530±335 € (p<0,001). Within existing supply structures, direct costing is a useful tool for economic comparison of different treatment services. Furthermore, temporal constraints of an economic bottleneck can be easily monitored and tackled with the help of time management tools.