Figure 3. Dose-dependent effects of ketamine in frozen hearts, on longitudinal and transverse ventricular conduction velocities at a pacing cycle length (PCL) of 1,000 ms (A, B, C). Panel D is designed to show that ketamine had no use-dependent effets (PCL of 400 ms). The closed circle represents the pacing site. Numbers indicate local activation times expressed in milliseconds. Isochrones are drawn at 10-ms intervals. The underlined activation times indicate the sites between which the longitudinal and transverse ventricular conduction velocities were measured in all panels. Increasing concentrations of ketamine progressively impaired longitudinal and transverse ventricular conduction velocity. The corresponding refractory periods are prolonged. Increasing the PCL did not enhance significantly the slowing of conduction velocities. No functional conduction block occurred, therefore no reentrant dysrhythmia could be induced. theta L = longitudinal ventricular conduction velocity; theta T = transverse ventricular conduction velocity. LAD = left anterior descending coronary artery.