You will find the article below interesting, and informative and I have tried to summarize the answer: Sinus bradycardia: A regular but unusually slow heart beat (60 beats/minute or less at rest). Sinus bradycardia can be the result of many things including good physical fitness, medications, and some forms of heart block. Sinus refers to the sinus node, the heart s natural pacemaker which creates the normal regular heartbeat. Bradycardia means that the heart rate is slower than normal. Fainting can occur with sinus bradycardia if the heart slows down even more. This can occur, for example, when the vagus nerve sends a signal to the heart that suddenly drops the heart rate. Choking or gagging can trigger this response which is called the vasovagal reflex. US President George W. Bush has sinus bradycardia and had an episode of fainting due to a vasovagal response after choking on a pretzel. Your heart muscle responds to an increased workload much like your arm muscles respond to weightlifting — by enlarging and thickening. As the muscle cells of your heart increase in size, the heart wall widens. However, unlike your biceps muscle, which rests when you put down the dumbbell, your heart muscle must work nonstop. Left ventricular hypertrophy may take up anywhere from weeks to years to develop. Over time, the heart muscle becomes stiff and the amount of blood that the heart can effectively pump out to the body begins to drop. Left untreated, the overdeveloped heart muscle will wear out and eventually fail. Left ventricular hypertrophy usually develops in response to excessive blood pressure (pressure overload) or excessive blood volume filling the left ventricle (volume overload). Pressure overload Causes of pressure overload include: * Hypertension. Blood pressure is determined by the amount of blood pumped by the heart and how the blood vessels respond to the pressure (resistance). High blood pressure is the most common cause of left ventricular hypertrophy. * Aortic stenosis. This is a condition in which there s a narrowing of the aortic valve, the flap separating your heart from the aorta, the large blood vessel that branches off your heart and delivers oxygen-rich blood to your body. When the aortic valve is narrowed, blood flow from the heart into the aorta and on to your body is obstructed. Aortic stenosis causes blood pressure to build in the left ventricle. Volume overload Causes of volume overload include: * Aortic valve regurgitation. Aortic valve regurgitation is a condition in which the heart valve separating the left ventricle and the aorta doesn t close properly, resulting in some blood flowing backward into the left ventricle. This increases the volume of blood in the left ventricle. * Dilated cardiomyopathy. Cardiomyopathy refers to a weakening of the heart muscle. The condition may be inherited or acquired later in life. Dilated cardiomyopathy involves the enlargement of one or more chambers of your heart. An enlarged left ventricle is able to fill with more blood and requires more force to pump it out to your body. Left ventricular hypertrophy can occur in the absence of pressure or volume overload. An inherited condition that causes a thickening in part or all of the heart (hypertrophic cardiomyopathy) can cause left ventricular hypertrophy. The above is and indicator of failing heart, and sudden death can ensue.