Fig. 3. A series of 20 sequential confocal x–y images obtained from a normal (MHN,  top ) and a malignant hyperthermia–susceptible (MHS,  bottom ) fiber mounted in parallel. At the beginning of the sequence, 1 mm halothane was introduced in the presence of 1 mm free Mg²⁺, and perfusion was stopped. Conditions were as described for  figure 1 , except 40 μm fluo-3 replaced fura-2. After a short delay, halothane caused a propagating Ca²⁺wave in the MHS fiber, whereas no response occurred in the MHN fiber. Frames were collected at 0.47 Hz.