Listening to Heart Sounds
Normal heart sounds are caused by the closure of the valves of the heart. These may be
heard by applying the ear to the chest wall of the subject or by listening through a
stethoscope.
The sounds heard can be likened to the following: LUB-DUP pause LUB-DUP pause. The
first heart sound (LUB) is caused by the closure of the left atrioventricular (bicuspid/mitral)
and right atrioventricular (tricuspid) valves at the onset of ventricular systole (contraction).
This sound may be augmented by the impact of the heart on the chest wall, which can be
felt in the 5th intercostal space (between the 5th and 6th ribs). This is known as the apex
beat.
The second heart sound, DUP, is caused by the closure of the aortic and pulmonary valves
at the beginning of ventricular diastole. It is shorter and sharper than the first. Since systole
is shorter than diastole (relaxation) there will be a pause between “DUP” and the following
“LUB”. Sometimes a third heart sound may be heard shortly after the second. It is due to
blood rushing into the ventricles during diastole.
Figure 4.5: Positions for Heart Sounds
Taken from Van Putte et al., 10th edition, Figure 20.20, p.690
If you have access to a stethoscope you can try this activity on a subject at
home. Otherwise please view the video on Blackboard to assist you.
1. Seat the subject and place the diaphragm of the stethoscope at the fifth intercostal
space, approximately 9 cm from the midline on the left (Figure 4.5). Listen for the
first heart sound.
2. Listen for the second sound at the second intercostal space, just to the left of the sternum.
3. See if you can identify the mitral (M) and tricuspid (T) components of the first sound, and
pulmonary (P) and aortic (A) components of the second sound, by placing the
stethoscope at the locations shown in Figure 4.5.
1
, The Electrocardiogram (ECG/EKG)
Cardiac muscle has the fundamental physiological property of automatic rhythmicity. This
feature is responsible for the uniformly paced alternating periods of depolarisation and
repolarisation of the heart that must precede the mechanical events of contraction and
relaxation of the heart muscle. In humans, the heartbeat is regulated by the sinoatrial (SA)
node or “pacemaker”, which is located in the wall of the right atrium.
Figure 4.6: Conduction System of the
Heart
Adapted from Van Putte et al., 11th
edition
Action potentials (AP) start in the SA node (labelled 1 in Fig 4.6 above) and travel across
the wall of the right atrium to the AV node (labelled 2). The AP then passes through the AV
node and along the AV bundle, which extends from the AV node into the interventricular
septum. The AV bundle divides into left and right bundle branches and action potentials
extend to the apex of each ventricle (labelled 3). APs are then carried by the Purkinje fibres
to the ventricular walls and papillary muscles (labelled 4).
In this activity we will be recording the electrical events of the heart during the cardiac
cycle with a view to linking them to their associated mechanical events. Records of the
electrical activity, or bioelectrical potentials, are made using an electrocardiograph.
Electrocardiographs are important tools in the diagnosis of many cardiac disorders.
Electrocardiographs amplify the electrical currents generated by the heart so that they are
strong enough to activate a recording device. The currents are conducted to the surface of
the body where they are picked up by recording electrodes attached to the
electrocardiograph. The amplified impulses can be recorded digitally or by use of a chart
recorder.
The record produced by the electrocardiograph is called an electrocardiogram
(ECG/EKG), which represents the sum of all the electrical events occurring in the heart at
that time. An ECG recording is shown in Figure 4.7 and a description of the features and
the major events is in Table 4.1.
Normal heart sounds are caused by the closure of the valves of the heart. These may be
heard by applying the ear to the chest wall of the subject or by listening through a
stethoscope.
The sounds heard can be likened to the following: LUB-DUP pause LUB-DUP pause. The
first heart sound (LUB) is caused by the closure of the left atrioventricular (bicuspid/mitral)
and right atrioventricular (tricuspid) valves at the onset of ventricular systole (contraction).
This sound may be augmented by the impact of the heart on the chest wall, which can be
felt in the 5th intercostal space (between the 5th and 6th ribs). This is known as the apex
beat.
The second heart sound, DUP, is caused by the closure of the aortic and pulmonary valves
at the beginning of ventricular diastole. It is shorter and sharper than the first. Since systole
is shorter than diastole (relaxation) there will be a pause between “DUP” and the following
“LUB”. Sometimes a third heart sound may be heard shortly after the second. It is due to
blood rushing into the ventricles during diastole.
Figure 4.5: Positions for Heart Sounds
Taken from Van Putte et al., 10th edition, Figure 20.20, p.690
If you have access to a stethoscope you can try this activity on a subject at
home. Otherwise please view the video on Blackboard to assist you.
1. Seat the subject and place the diaphragm of the stethoscope at the fifth intercostal
space, approximately 9 cm from the midline on the left (Figure 4.5). Listen for the
first heart sound.
2. Listen for the second sound at the second intercostal space, just to the left of the sternum.
3. See if you can identify the mitral (M) and tricuspid (T) components of the first sound, and
pulmonary (P) and aortic (A) components of the second sound, by placing the
stethoscope at the locations shown in Figure 4.5.
1
, The Electrocardiogram (ECG/EKG)
Cardiac muscle has the fundamental physiological property of automatic rhythmicity. This
feature is responsible for the uniformly paced alternating periods of depolarisation and
repolarisation of the heart that must precede the mechanical events of contraction and
relaxation of the heart muscle. In humans, the heartbeat is regulated by the sinoatrial (SA)
node or “pacemaker”, which is located in the wall of the right atrium.
Figure 4.6: Conduction System of the
Heart
Adapted from Van Putte et al., 11th
edition
Action potentials (AP) start in the SA node (labelled 1 in Fig 4.6 above) and travel across
the wall of the right atrium to the AV node (labelled 2). The AP then passes through the AV
node and along the AV bundle, which extends from the AV node into the interventricular
septum. The AV bundle divides into left and right bundle branches and action potentials
extend to the apex of each ventricle (labelled 3). APs are then carried by the Purkinje fibres
to the ventricular walls and papillary muscles (labelled 4).
In this activity we will be recording the electrical events of the heart during the cardiac
cycle with a view to linking them to their associated mechanical events. Records of the
electrical activity, or bioelectrical potentials, are made using an electrocardiograph.
Electrocardiographs are important tools in the diagnosis of many cardiac disorders.
Electrocardiographs amplify the electrical currents generated by the heart so that they are
strong enough to activate a recording device. The currents are conducted to the surface of
the body where they are picked up by recording electrodes attached to the
electrocardiograph. The amplified impulses can be recorded digitally or by use of a chart
recorder.
The record produced by the electrocardiograph is called an electrocardiogram
(ECG/EKG), which represents the sum of all the electrical events occurring in the heart at
that time. An ECG recording is shown in Figure 4.7 and a description of the features and
the major events is in Table 4.1.
