In the Madison Symmetric Torus reversed-field pinch, ions are impulsivelyheated during a sawtooth crash; the ion temperature more than doubles. Heatingappears to be nearly isotropic; the impurity ion temperature measuredperpendicular to the magnetic field (T⊥) is approximately equal to impurityion temperature parallel to the magnetic field (T∥) during a sawtoothcrash. Ion heating occurs simultaneously throughout the entire plasma volume,with no non-Maxwellian distortion of the ion velocity distribution function.