Learn Farsi: در حیاط گشت می‌زدم که تپش قلبم شدید شد. - I was patrolling the courtyard when my heartbeat became intense.

This is the narrative interruption structure. When you have a background action in the Past Continuous (gasht mi-zadam, meaning I was patrolling) followed by ke, it introduces a sudden, interrupting event in the Simple Past (shadid shod, meaning became intense). In this specific pattern, ke acts like "when suddenly".

Is gasht zadan only used for security or police "patrolling"?

Not always. While it does mean to patrol, in everyday Farsi gasht zadan is also frequently used for strolling, wandering, or pacing around an area. Depending on the broader context, the speaker might just be taking a restless walk in the courtyard.

How do the word endings work in the phrase tapesh-e qalb-am?

This phrase links two nouns and a possessive suffix. tapesh (beating) is linked to qalb (heart) using the connecting vowel known as an ezâfe. The possessive suffix -am (my) attaches to the very end of this noun chain. It literally translates to the beating of heart-my.

Why use shod instead of bud at the end of the sentence?

shod is the Simple Past of shodan (to become) and it emphasizes the sudden change of state triggered by the interrupting event after ke. If you used bud (was), it would simply describe a static, ongoing state rather than the sudden spike in heart rate that interrupted the walk.