Effects on the heart and circulation

• Tachycardia: persistent resting sinus tachycardia and exaggerated heart-rate response to exertion.
• Increased contractility and cardiac output: increased stroke volume, heart rate, and myocardial oxygen consumption. Cardiac output may rise substantially.
• Reduced systemic vascular resistance: peripheral vasodilation lowers diastolic blood pressure.
• Wide pulse pressure: systolic pressure may rise while diastolic pressure falls.
• Palpitations and ectopic beats: common due to increased sympathetic sensitivity.
• Atrial fibrillation: especially in older adults or people with underlying heart disease. It increases risk of thromboembolism and stroke.
• Other tachyarrhythmias: atrial flutter or supraventricular tachycardia may occur; ventricular arrhythmias are less common unless cardiac disease is present.
• Angina or myocardial ischemia: hyperthyroidism raises myocardial oxygen demand and can unmask coronary artery disease.
• Heart failure: sustained tachycardia, atrial fibrillation, or pre-existing cardiac disease can lead to high-output heart failure. In severe untreated thyrotoxicosis, dilated cardiomyopathy and reduced ejection fraction can occur, often improving after treatment.
• Functional systolic murmurs: increased flow can produce an ejection systolic murmur.

Typical clinical clues

Key point