Several algorithms for quantitative analysis of 201Tl scintigrams require operator assigned elliptical regions. Therefore these algorithms are hampered by inter- and intra-observer errors. In this paper we present a robust algorithm to determine automatically contours with elliptical shapes. The algorithm is based on the Hough transformation and can determine the parameters describing an ellipse even in low signal-to-noise ratio images and when the contour is only partially visualized such as in non-perfused regions of the left ventricular myocardium. As long as the number of parameters to describe the shape of the contour is not too large, the same kind of algorithm can also be used for differently shaped contours, and for 3D elliptical contours as in SPECT.