Fetching details from the dictionary...

peace of mind; relief; (sense of) security; safety; assurance; confidence
「安心」 has another reading with different meanings.
試験に受かって安心した。
I was relieved to pass the exam.
試験が終わって、やっと安心しました。
The exam is over, and I finally feel relieved.
試験が終わって、安心します。
I felt relieved after the exam ended.