Using the Spanish preterite tense combined with cuando + the Spanish imperfect tense

We use El Pretérito Indefinido for a new action in the past, which interrupts another action that was already taking place.
Read and listen to these examples:

In the examples above, the subordinate clause introduced by cuando uses El Pretérito Imperfecto in order to indicate that an action was already happening, while the verb in main clause is in El Pretérito Indefinido to express the newly-begun action.

See also:

• El Pretérito Indefinido
• El Pretérito Imperfecto