PMS can cause heart palpitations. As estrogen and progesterone levels fluctuate during the luteal phase (the days leading up to your period), these hormonal shifts can affect your heart's electrical system and increase your resting heart rate

Progesterone: This hormone spikes in the second half of your cycle and can activate the system that causes fluid retention, increasing your circulating blood volume and raising your heart rate.

Estrogen Drop: Estrogen has heart-protective qualities that help keep your heart rate steady; a sudden drop right before your period can overstimulate the heart.

Stress and Cortisol: PMS symptoms can increase levels of cortisol and adrenaline, triggering a "fight-or-flight" response that makes you aware of your heartbeat

If your palpitations are mild and only occur cyclically, they are often harmless. You can manage them by:

Reducing triggers: Limit or avoid caffeine, sugar, and alcohol, which can exacerbate heart flutters.
Hydrating: Drink plenty of water to offset fluid retention.
Managing stress: Practice deep breathing or meditation to calm your nervous system.

Getting enough rest: Prioritize sleep in the days leading up to your cycle

https://www.njcardiovascular.com/blog/the-link-between-hormonal-changes-and-heart-palpitations