Thyroid hormones stimulate a faster heart rate and a stronger contraction of the heart muscle. (chai-online.org)
During inspiration, there occurs an acceleration of the heartbeat, a decrease in force of contraction of the heart muscle and an increase in the loudness of the heart sounds. (si.com)
The resulting rhythmic signals produced by this transfer of cations are what support the synchronous contraction of our heart muscles and neuronal firing in parts of the brain, like the thalamus, which helps regulate our sleep - wake cycle, or circadian rhythm. (sciencedaily.com)