It's good to trust your doctor. If you are concerned, maybe seek a 2nd opinion. Also, get back to exercising. It is encouraging that you raised your heart strength that much with exercise. Good luck.
Heart Rate is iun beats per minute with a "normal" rest range of 60 to 100. It is never expressed as a %.
Perhaps you are saying you had a HR of 38 at rest and this is well below normal, clearly in the Bradycardia range. If you then got it up to 52, at rest again, you closer to normal and that is alright for some people. Most would find this rate too low to be able to make sudden changes in activity level without getting dizzy. Here I assume you HR goes up when you are up and active physically.
I am not posting to argue with your doctor, I am not qualified to do that. Still, if you are saying you HR is again back in the 30-something BPM, I consider that very low. For example can you sit and read or watch TV and then get up quickly to answer the door or the telephone in the next room without getting dizzy? If you don't get dizzy when you suddenly stand up and start walking quickly you have indeed become accustom to the lower HR. And again I am taking your % to mean BPM.
You state in your title that you have a low heart rate but describe your issue in % which is more related to ejection fraction rate. Are you clear on whether the doctor was describing your heart rate or ejection fraction. This could very well determine how troubling your issue really is. I would think a slow heart rate would be not quite as troubling as a low ejection fraction that said, I would assume you are being treated for your heart failure. Please do not stop doing so. In any event I didn't know much about ejection fraction so I looked it up and found this off the Cleveland Clinic website.
What is ejection fraction?
Ejection fraction is a test that determines how well your heart pumps with each beat.
Left ventricular ejection fraction (LVEF) is the measurement of how much blood is being pumped out of the left ventricle of the heart (the main pumping chamber) with each contraction.
Right ventricular ejection fraction (RVEF) is the measurement of how much blood is being pumped out of the right side of the heart to the lungs for oxygen.
In most cases, the term “ejection fraction” refers to left ventricular ejection fraction.
Ejection Fraction Measurement What it Means
40-55% Below Normal
Less than 40% May confirm diagnosis of heart failure
<35% Patient may be at risk of life-threatening irregular heartbeats
What do the numbers mean?
Ejection fraction is usually expressed as a percentage. A normal heart pumps a little more than half the heart’s blood volume with each beat. (1)
A normal LVEF ranges from 55-70%. A LVEF of 65, for example, means that 65% of the total amount of blood in the left ventricle is pumped out with each heartbeat.
The LVEF may be lower when the heart muscle has become damaged due to a heart attack, heart muscle disease (cardiomyopathy), or other causes.
An EF of less than 40% may confirm a diagnosis of heart failure. Someone with diastolic failure can have a normal EF.
An EF of less than 35% increases the risk of life- threatening irregular heartbeats that can cause sudden cardiac arrest (loss of heart function) and sudden cardiac death. An implantable cardioverter defibrillator (ICD) may be recommended for these patients.
Your EF can go up and down, based on your heart condition and the therapies that have been prescribed.
How is EF measured?
EF can be measured in your doctor’s office during tests such as:
Ultrasound of the heart (echocardiography) – used most often
Magnetic resonance imaging (MRI) scan of the heart
Nuclear medicine scan (multiple gated acquisition or MUGA) of the heart; also called a nuclear stress test
Computerized tomography (CT) scan of the heart
What is heart failure?
Heart failure means:
The muscles of the heart are weaker than normal or the lower chambers of the heart are not able to relax and fill with blood as they normally do
Less blood is pumped out of the heart to organs and tissues in the body
Pressure in the heart increases
Heart failure does not mean that your heart has stopped working.
When the heart cannot pump enough oxygen and nutrients to meet the body’s needs, it tries to adapt. The chambers of the heart stretch to hold more blood to pump through the body with each heartbeat. Hormones are released into the bloodstream to increase the heart’s pumping power and increase blood flow into the heart chambers. These changes provide temporary relief, but over time, the heart muscle walls continue to weaken and/or stiffen.
There are two types of heart failure:
Systolic left ventricular dysfunction (or systolic heart failure) occurs when the left ventricle heart muscle doesn't contract with enough force, so less oxygen-rich blood is pumped throughout the body.
Heart failure with preserved left ventricular function (diastolic heart failure) occurs when the heart contracts normally, but the ventricles do not relax properly or are stiff and less blood enters the heart during normal filling. In this case, the ejection fraction may be normal.
Why It’s Important to Know Your EF
If you have a heart condition, it is important for you and your doctor to know your EF.
Your EF can help your doctor determine the best course of treatment for you and the effectiveness of the therapies that have been prescribed.
You should have your EF measured initially when you are first diagnosed with a heart condition, and again as needed, based on changes in your condition. Ask your doctor how often you should have your EF checked.
This all said, has a pacemaker or ICD been recommended? Do you notice any irregular beats, skipping jumping or fluttering? If so please do inform your doctor about this and again make sure you continue to follow your doctor's advice to ensure your heart stays as healthy as possible for as long as possible. I think in your case it would be really important to know if your issue is a low ejection fraction or slow heart rate and what the health risk difference is in your case. Ask your doctor where your health stands and what risks you are under so you are fully prepared and aware of what is going on with you and what steps you need to take to ensure the best long term health for your heart.
The one last thing I will say about heart rate, I had an svt that caused my heart to beat really fast from time to time. I think because of it and being a small person I had a normally fast heart beat generally in the high end of normal. After I got the svt corrected and began an exercise routine my normal heart rate did lower. As it did I noticed for a time that it would hurt a slight bit but after a while the discomfort went away. As well now when it goes higher I can feel discomfort because I am not use to it being as high as it was. So to answer your initial question in my cased it does seem as though the body does have the ability to adjust. But please do inform your doctor of any changes you are experiencing as you move forward. Take care and I wish good health to you.
Yes, ejection fraction, that's it as it was explained to me by the doctor. I just missed the name of it. Thank you for your response, it was very helpful. And yes, a Dr. in NYC did threaten me with a pacemaker if I didn't get some exercise. I HAVE become more active, but I haven't been tested since being back home. I'm especially concerned because of the mucus in my lungs 24/7. Doctors have told me that it's asthma, which I'd never had before. I've been briefly treated for asthma with prednisone, but doctors all agree that the side effects are worse than the disease, so that was stopped. Although a chest x-ray ruled it out years ago, the mucus MIGHT even be pulmonary edema. One doctor even suggested sleep apnea. Regardless of what it really is, all the coughing might make a weak heart even worse. Since I don't have very exciting health insurance, doctors tend to blow me off, so I have to do research on sites like this. Thanks again.