bradycardia

antonym: tachycardia
https://doi.org/10.1351/goldbook.11645
Abnormally slow heart rate.
Compare: tachycardia
Source:
PAC, 2015, 87, 841. (IUPAC Glossary of terms used in neurotoxicology (IUPAC Recommendations 2015)) on page 853 [Terms] [Paper]