Atenolol (Tenormin) for Pets in 2025: Vet Guide to Safe Heart Rate & Blood Pressure Control 🐶🐱❤️

By Dr Duncan Houston, BVSc
Updated July 2025

💡 Atenolol, a selective beta‑1 blocker commonly known as Tenormin®, is used in veterinary cardiology to manage conditions such as subaortic stenosis, hypertrophic cardiomyopathy, certain arrhythmias, and hypertension. This 2025 guide explains its mechanism, applications, side effects, drug interactions, and safe use strategies for cats and dogs.

🫀 What Does a Beta‑1 Blocker Do?

Taken from the sympathetic “fight‑or‑flight” response: beta‑1 receptors in the heart increase rate & strength when stimulated. Atenolol blocks these, calming the heart, reducing stress on cardiac muscle, and improving filling time.

📌 When Atenolol Is Used

• Subaortic stenosis (dogs): slows heart and helps manage obstruction.
• Hypertrophic cardiomyopathy (cats): slows heart so thicker chambers fill better.
• Supraventricular tachycardia & other arrhythmias: slows overly fast rhythms.
• Hypertension: may also lower blood pressure.
• Pre‑thyroidectomy in cats: helps manage the heart during treatment.

⚙️ Administration & Timing

• Available in 25, 50, 100 mg tablets under brand Tenormin®
• Typically dosed twice daily, with or without food
• Do not skip doses—if you do, resume normal schedule
• Store at room temperature, away from light
• Abrupt discontinuation can lead to rebound tachycardia—taper over 1‑2 weeks if stopping

⚠️ Side Effects to Watch For

These are typically mild:

• Listlessness, mild diarrhea or vomiting—usually temporary
• Serious: excessive heart rate/blood pressure drop, fainting—discontinue and contact vet
• Atenolol can interfere with blood sugar control in diabetics
• Because it's β‑1 selective, it usually does not interfere with lung function—but use cautiously in asthmatic pets

🔄 Drug Interactions

• Sympathetic stimulants: phenylpropanolamine, terbutaline may counteract atenolol
• Increased hypotension risk: with other BP-lowering drugs like prazosin, amlodipine, acepromazine
• Antacids: reduce absorption—give hours apart
• Furosemide: may worsen glucose control effects

⚙️ Use in Special Populations

• Do not use in heart failure: needing strong cardiac output
• Kidney disease: avoid or monitor closely
• Diabetes: may mask signs of hypoglycemia

📲 Ask A Vet App Support

Need guidance on heart monitoring, dose adjustments, or tapering protocols? The Ask A Vet app offers:

• 🩺 Personalized tapering advice to stop atenolol safely
• 📊 Strategies for monitoring heart/blood pressure at home
• ⚠️ Drug interaction checks & diabetic safety guidance

➡️ For cardiac support in pets, download the Ask A Vet app. Visit AskAVet.com.

✅ Final Takeaways from Dr Duncan Houston

• Atenolol is a focused and effective heart-rate controller in cats & dogs.
• Always dose twice daily, never stop abruptly, and monitor for low heart rate or blood pressure.
• Side effects are generally mild but diabetic cases require extra care.
• Regular check-ins with your vet and Ask A Vet support ensure safe long-term use.

🐾❤️ When used responsibly, atenolol offers meaningful benefits for pets with heart or blood-pressure issues—but only under veterinary supervision and careful monitoring. Use Ask A Vet for expert guidance throughout treatment.