A three-dimensional display is described that allows activation sequences from the epicardium and endocardium to be shown simultaneously on the same image. Three electrode arrays (epicardial sock, left ventricular balloon, right ventricular balloon) are represented in a three-dimensional perspective by an array of dots that are intensified when activated. This arrangement requires fewer calculations and is easier to interpret than sliced-isochronal maps but cannot represent a complete heart cycle in one image. The three-dimensional display eliminates the distortion caused by two-dimensional diagrams and facilitates activation correlation between electrode arrays. A standard, low cost microcomputer has been used to implement the activation display.