- The first heart sound (S1) is heard as the atrioventricular valves close and is heard loudest at the apex of the heart.
- The second heart sound (S2) is heard when the semilunar valves close and is heard loudest at the base of the heart.
Hear normal and abnormal heartbeats.
- A third heart sound (S3) may be heard if ventricular wall compliance is decreased and structures in the ventricular wall vibrate; this can occur in conditions such as congestive heart failure or valvular regurgitation. However, a third heart sound may be normal in individuals younger than 30 years.
- A fourth heart sound (S4) may be heard on atrial systole if resistance to ventricular filling is present; this is an abnormal finding, and the causes include cardiac hypertrophy, disease, or injury to the ventricular wall.
- The faster the heart rate, the less time the heart has for filling, and the cardiac output decreases.
- An increase in heart rate increases oxygen consumption.
- The normal sinus heart rate is 60 to 100 beats/min.
- Sinus tachycardia is a rate more than 100 beats/min.
- Sinus bradycardia is a rate less than 60 beats/min.