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Dr.Fiona, Cat Veterinarian
Category: Cat Veterinary
Satisfied Customers: 6273
Experience:  Small animal medicine and surgery - 16 years experience in BC, California and Ontario
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My 19 year old male cat has a very fast heart beat. Was at

Resolved Question:

My 19 year old male cat has a very fast heart beat. Was at vets today. He's hyperthyroid. What should I give him to slow down his heart beat? Lasix, Methimazole or Enalapril? He had liquid in his belly as well. Please advise.
Submitted: 7 years ago.
Category: Cat Veterinary
Expert:  Dr.Fiona replied 7 years ago.

Hi there,

Welcome to Just Answer! I would like to help you and your cat with this question, but need a bit more information in order to better assist you.

When was he diagnosed with hyperthyroidism?

What is his heart rate?

How many breaths per minute is he taking?

How many hours since he was at the vet?


Customer: replied 7 years ago.
Diagnosed today. He was there this afternoon - 8 hours ago (LA time). Heart beat is fast. He is eating and peeing a lot. Trying to sleep. Breathing is pretty steady, even.
Expert:  Dr.Fiona replied 7 years ago.
Have you started him on the methimazole yet?

I assume that this was prescribed for him, but wondered if you have given a dose yet?

Did the vet mention the fast heart beat, or is that something you are noticing at home?
Customer: replied 7 years ago.
Yes, this afternoon. Should I give him another dosage?
Expert:  Dr.Fiona replied 7 years ago.
No, don't give another dose of methimazole! If you give too much it is likely to cause him to vomit. Not only will that be unpleasant for him, but also it will mean he does not absorb his medication.

With hyperthyroidism, it can take about 2 weeks for thyroid levels to return to normal, and thus for heart rate to return to normal. Hyperthyroidism is something that comes on slowly, and it is easiest on the body if we lower the thyroid levels gradually so as to avoid complications (like vomiting or loss of appetite).

Has your vet had a chance to tell you more about hyperthyroidism?

In case he or she has not, let me explain....

Hyperthyroidism is a fairly common disorder of older cats in which the thyroid gland in the neck starts to over-produce a hormone called T4. T4 controls metabolic rate. So, the more you have of it, the faster the metabolism.

Cats that are hyperthyroid tend to eat well, but eventually start to lose weight because they burn the calories up so fast. Their heart rates increase, and the transit time through the intestines increases. So, they may develop diarrhea and vomiting, but not always.

A classic symptom is increased meowing.

Hyperthyroidism can be diagnosed by physical exam and blood and urine analysis. On a physical exam, I check for enlarged thyroid glands, and a rapid heart rate, and sometimes heart murmurs. Blood and urine tests allow a vet to confirm the diagnosis.

Hyperthyroidism responds really well to treatment.

There are 3 treatment options.

THey are:

1. Methimazole (tapazole is the trade name) given orally OR transdermally (a paste applied to the ear).

This medication is given usually once or twice daily, always for the rest of kitty's life.

Here is more about it:

2. Surgery to remove the overactive thyroid gland.

This is a tricky surgery, and not one that I have done myself. However, there are many older veterinarians who are very good at this surgery – as they had to be when we didn’t have other treatment options.

The tricky part is that the thyroid is RIGHT beside the parathyroid. And while you can safely remove a thyroid gland, there can be serious consequences with blood calcium levels if you accidentally damage the parathyroid gland.

So, you might have to look around for a vet who does this surgery. When I worked in California, my boss there did this surgery quickly and well. It cost about $500.

Here is more about it: and here:

3. Radioactive iodine treatment (this last is the BEST treatment because it gives you a cure, but it is expensive). The cat has to spend about 1 week at a treatment facility that specializes in this service. In a perfect world where we did not have to consider cost, this would be the best option for almost every hyperthyroid cat! More here:

So, as you can can see, there are a number of treatment options. Most cats do really well with the medication which is what you have there.

Here is more about hyperthyroidism:

In terms of what you can do to help your old boy:
1. Give the methimazole as prescribed - giving more will likely lead to side effects like vomiting or loss of appetite.

2. Lasix will make the cat urinate more and may lead to dehydration if given in excess, so I would not recommend this be increased. When a cat has fluid in the lungs, and is struggling to breathe, this drug can rapidly move the fluid out so cat can breathe better. It does NOT lower heart rate.

3. Enalapril is an "ace inhibitor" which helps the heart to function better and helps to lower blood pressure. We would not want to give excess of this, either as it could drop the blood pressure dangerously low.

So, for your kitty, I would try to:
1 keep him calm and relaxed.
2. You could safely give him cat nip (this has a relaxing effect on many cats) or
3. you could give rescue remedy.

More about it here:

It is pretty widely available at health food stores. If you don't have one near you, here is a link:

I have found the results variable with Rescue remedy. Some cats do seem more relaxed with Rescue Remedy, some don't seem to have any change with its use. But it is safe!

I do hope that this helps you to help your senior cat!

If this has been helpful, please "Accept" my answer and provide feedback.

If you need more information, just click on reply and I will try to provide it!

The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.


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