If you are not used to regular physical activity, you can put extra stress on your heart. This can lead to an acute heart attack. So, it is advisable to begin your fitness journey slowly.
One of the possible reasons is the underlying disease such as coronary artery disease (CAD), which narrows the blood vessels supplying the heart muscle. Exercise can stress your heart if you push yourself hard and if there's reduced blood flow due to blockages in these vessels, it can trigger a heart attack.
Never be on the treadmill if you are stressed as it causes a surge in stress hormones like adrenalin, which can put extra strain on your heart.
Inadequate hydration can lead to thicker blood, making it harder for the heart to pump which in as a result can trigger a cardiac event.
Warm-up is necessary as sudden, intense activity can increase heart rate and blood pressure, which can strain the heart.
Poor treadmill usage such as excessive speed and improper posture can strain the heart.