I've been experiencing a rapid heartbeat and palpitations with no specific timing. Sometimes it feels like my heart is sinking. I've had an ECG and TMT, and both came back normal. I also have hypothyroidism, and my doctor thinks it might be due to anxiety. I'm wondering if I should get any other tests to rule out heart disease. What do you think?

Based on your symptoms and the normal ECG and TMT results, it is likely that your palpitations and fast heart rate are indeed related to anxiety, especially given your history of hypothyroidism. However, if you still have concerns about ruling out any underlying heart disease, you may consider getting a Holter monitor test to monitor your heart rhythm continuously for a period of time. This can help detect any irregular heartbeats that may not show up on a standard ECG. Additionally, an echocardiogram may be considered to assess the structure and function of your heart. In the meantime, managing your anxiety through relaxation techniques, regular exercise, and stress-reducing activities can also help alleviate your symptoms.