Heart Rate Too Fast or Too Slow: Tachycardia and Bradycardia Explained

Normal resting heart rate: 60–100 bpm.

Tachycardia (>100 bpm)

Causes: anxiety, exercise, fever, caffeine, nicotine, alcohol, medications (stimulants, thyroid hormone), anemia, hyperthyroidism, heart failure, arrhythmias (SVT, AFib, VT).

Bradycardia (<60 bpm)

Causes: athletic conditioning, beta-blockers/calcium channel blockers/digoxin, hypothyroidism, electrolyte imbalance (high K⁺), heart block, increased intracranial pressure.

When to Seek Care

• Symptomatic (dizziness, syncope, chest pain, dyspnea, confusion).
• Persistent unexplained tachycardia/bradycardia.
• Known heart disease with new rate changes.

Both can be serious; evaluation includes ECG, labs, monitoring.