Advent Health explains that when you drink coffee, the caffeine in it enters your bloodstream through your stomach and small intestine. Once it enters your body, it begins to stimulate your nervous system. Receptors in your heart cells are stimulated as well, causing your heart to beat faster. Your blood flow speeds up too. They note that these effects take about six hours to wear off.
UC Davis Health writes that healthy people tolerate these effects well, but for some people, especially those with heart problems or high blood pressure, the caffeine found in coffee can be a problem. It can lead to heart palpitations or extra heartbeats. It can also cause atrial fibrillation and rapid heartbeat. According to Mayo Clinic, some people who drink caffeinated beverages regularly also tend to have higher average blood pressure. If blood pressure is too high, it can force the heart to work harder, damaging it over time and leading to heart failure. High blood pressure can additionally contribute to coronary artery disease since it causes the arteries that supply the heart to become damaged and narrowed (per Mayo Clinic).