Question: what does it mean when you see your ex and your heart starts beating fast?
Answer: It's a natural little “stress” reaction. It also happens when people get startled, surprised, and when you suddenly see or get a call from your ex or someone you're crushing on. It's part of the “fight or flight” response we all instinctively have. ... It's part of the “fight or flight” response we all instinctively have.