The Human Cardiovascular System - Computational Hemodynamics: Theory, Modelling and Applications - page 25

Fig. 2.5 A magnetic reso-
nance showing how the heart
is positioned in a human. The
image shows a slice through
all the four heart chambers
during ventricular filling. The
image is seen from the feet so
the right side in the picture is
the subjects left side . The MR
acquisitions were performed
at St. Olavs University
Hospital, Trondheim. (Image
from Dahl 2012)

pulmonary, mitral and aortic valves of the heart ensure that blood flows in the
circulatory system effectively without reversing its direction in the circuit.
The magnetic resonance image in Fig. 2.5 shows a slice through all four heart
chambers during ventricular filling. The subject is lying supine and the image is
seen from the feet which mean that the right side in the picture is the subjects left
side. Fig. 2.2 shows the heart situated in the chest cavity in between the two lungs
and behind and slightly left of the sternum (breastbone). The narrow end of the heart
is called the apex and the broad end is called the base. The apex is pointing down-
wards and to the left, whereas the base is directed upwards and to the right. The left
ventricle, the right ventricle, the left atrium and the right atrium (RA) are indicated
in the scanned image.

2.2.2 Cardiac Cycle 1

The sequence of events that occur in the heart during one heart beat is called the car-
diac cycle. The events occur nearly simultaneously for both sides of the heart. The
typical resting heart rate in adults is 60-90 beats/min (bpm). A physically fit person
has a lower heart rate compared to an inactive person. Each heart beat is commonly
divided into two main phases: systole and diastole. Systole and diastole are syn-
onymous with contraction and relaxation of a heart muscle, respectively. Both the

1 Contribution from Dahl, S.K. (2012) Numerical Simulations of Blood Flow in the Left Side of
the Heart. PhD Thesis, Norwegian University of Science and Technology.