Researchers advise that people who suffer from epilepsy or seizures should ask for professional insight first before using binaural beats. Pregnant women are also advised to seek the advice of their physicians. However, I haven’t heard anything about binaural beats impacting those who have had heart attacks negatively. That being said, I encourage you to do extra research.

Words could be great stress relievers. One technique to quell sudden stress is to repeat a phrase from which you draw power and strength. “Think positively about releasing what is bothering you by repeating a positive mantra that uplifts you such as, ‘I am at peace,’ ‘All is well,’ ‘I choose to think thoughts that serve me,’ or ‘I love and believe in myself fully,’” says Carol Whitaker, life transformation expert and the author of Ridiculously Happy! The Secret to Manifesting the Life and Body of Your Dreams. “This too shall pass” is another good one. Repeating a mantra is actually a type of meditation that can make you more resilient to stress—some studies show it can actually alter your brain’s neural pathways. You can place reminders of your mantras near the places you tend to get stressed, like your work space. “I actually keep a file on my computer of great quotes and inspiring sayings. So when I’m feeling overwhelmed by life’s struggles, I clip them to my screensaver, post them on my social media, and even print them out to put on my refrigerator or desk,” Dr. Serani says.
From a brainwave entrainment effectiveness perspective, it’s my understanding that the response from isochronic tones stimulation starts to diminish over 30Hz and that 40Hz is about the limit for using them. So from what I’ve read on the topic a 100Hz beat wouldn’t work, probably because it’s too fast for the brain to process and synchronise with it.
Different people have different requirements when it comes to frequency changes in the music and it's quite impossible for us to anticipate them all. We would need to produce so many different variants of all our music productions that it would be impractical to manage and confusing for our customers. For example, if we were to start raising the frequency from theta up to alpha between the 50-60 minute mark of a piece of music, this would be useless to someone who used the music for a guided meditation that was only 45 minutes long. In the early stages of the development of our brainwave entrainment music we had so many different requests from different people that we could only opt for the simplest solution, which is to use a consistent frequency throughout. It might not be the absolute "perfect ideal", but this is still a very effective technique and the feedback we've received on our brainwave entrainment music has always been exceptionally positive.
Absolutely. Binaural beats were first discovered over 150 years ago, and their use in brainwave entrainment audio has been the subject of a great deal of scientific exploration over the last 35 years in particular. Millions of people use brainwave entrainment music to enhance their quality of life and to experience deep relaxation. In fact, brainwave entrainment technology is now used for more than just meditation. It is also used by a variety of practitioners and private users for improving self-confidence, stress relief, pain management, relaxation, improving and concentration and improving the quality of one's sleep. If you would like to read an objective third party report on binaural beats, please refer to this Wikipedia article.
“Binaural beats are not very noticeable because the modulation depth (the difference between loud and quiet) is 3 db, a two-to-one ratio. (Isochronic tones and mono beats easily have 50 db difference between loud and quiet, which is a 100,00-to-1 ratio). This means that binaural beats are unlikely to produce an significant entrainment because they don’t activate the thalamus.”

A potential and generally desired result of brainwave entrainment is hemispheric synchronization. It refers to a state when the brainwave pattern of the right and left hemispheres become alike. It is said that a person with similar activity in both hemispheres tend to be happier, more optimistic and more emotionally stable and less prone to mental illness. Studies found that increased levels of synchronization are found naturally in people who meditate regularly and people who are very happy with their lives in general.
Aside from Brain Evolution, this is another good resource for brainwave entrainment products that I recommend. They have binaural beats and isochronic tones for many different applications. The nice thing is that they are inexpensive, so you can experiment with different types and find ones that work for you. They also have a membership plan that makes experimenting even more affordable. It’s probably the best bang for the buck that I can find for brainwave entrainment.
Theta brainwaves occur most often in sleep but are also dominant in deep meditation. Theta is our gateway to learning, memory, and intuition. In theta, our senses are withdrawn from the external world and focused on signals originating from within. It is that twilight state which we normally only experience fleetingly as we wake or drift off to sleep. In theta we are in a dream; vivid imagery, intuition and information beyond our normal conscious awareness. It’s where we hold our ‘stuff’, our fears, troubled history, and nightmares.
It may be that you had the volume too loud, but I would expect you to hear the effects of that straight after you’ve stopped listening, not on a day you haven’t used them. It might be something similar to muscle memory, where you suddenly remembered the sound and sensations it gives you as if you were hearing it again. I don’t know how long you’ve been using this type of thing for, but maybe it’s something that will settle down and disappear once you become more accustomed to the sound.
When you play two separate frequencies in each ear, say 140 Hz and 149 Hz, the difference in frequency is 9 Hz. Your brain compensates for this difference and a third tone of 9 Hz is experienced. This will result in your brain being lowered or raised and tuned into the desired frequency. This is how binaural beats are produced. Headphones are essential for this to work.  
The functional role of neural oscillations is still not fully understood;[6] however they have been shown to correlate with emotional responses, motor control, and a number of cognitive functions including information transfer, perception, and memory.[7][8][9] Specifically, neural oscillations, in particular theta activity, are extensively linked to memory function, and coupling between theta and gamma activity is considered to be vital for memory functions, including episodic memory.[10][11][12]