Problems with your heart beating too quickly, skipping a beat, or not beating with a steady rhythm are called "heart palpitations".

You use the phrase "heart palpitations" when describing this feeling to a doctor or nurse, or when telling someone about your medical problems.

If your heart beats strangely because of a strong emotion like fear or excitement, it's more common to use phrsases like "my heart was racing" or "my heart skipped a beat".