I bet your issue has more to do with your mind getting stuck obsessing about the sensation, whether it is the tinnitus or the sound of your heartbeat.

Once the brain gets tuned into a sensation, it can increase the sensitivity of that sensory system. Actually, the sensitivity is not increased. The system that filters out sensations get over-ridden so rather than the brain tuning out and ignoring the sensation, the brain focuses on the sensation.

It is like playing slug bug. Once you start looking for VW bugs, even when you stop looking for them, your brain continues to notice them.