most "heart failure" is a result of a long history of uncontrolled high blood pressure. Heart attacks are usually the result of clogged arteries. If you have electrical issues you can have a bout of ventricular fib and that can kill young people. You do not say how long you have been training. As you become fitter and your vascular system becomes more developed and your stroke volume increases (and it will) your heart rate at a given power output will get lower. Of course when this happens your power output will increase.

Just to be safe you should have a cardiologist do a treadmill stress test to make sure there are no EKG issues. At 26 you are probably ok but young athletes have dropped dead due to undiagnosed issues.