A	Aortic cross section, cm2
AC	Aortic valve closure
AO	Aortic valve opening
BCG	Ballistocardiography
C	Length of one heart cycle, s
ECG	Electrocardiography
F	Pre-systolic wave of the longitudinal acceleration BCG signal
G	Pre-systolic wave of the longitudinal acceleration BCG signal
H	Pre-ejection upward wave of the longitudinal acceleration BCG signal
HF	High frequency
HRV	Heart rate variability
I	First post-ejection downward wave of the longitudinal acceleration BCG signal
IVC	Isovolumetric contraction
J	First post-ejection upward wave of the longitudinal acceleration BCG signal
K	Second post-ejection downward wave of the longitudinal acceleration BCG signal
LF	Low frequency
MC	Mitral valve closure
MO	Mitral valve opening
MRI	Magnetic resonance imaging
NN	Normal-to-normal interval
P	ECG wave representing the electrical depolarization of the atria of the heart
PCG	Phonocardiography
pNN50	Proportion of the successive pairs of NN intervals that differ more than 50 ms divided by the total number of NN intervals
Q	ECG wave representing the normal left-to-right depolarization of the interventricular septum
R	ECG wave corresponding to depolarization of the main mass of the ventricles
RE	Rapid ejection
RF	Rapid filling
RMSSD	Root mean square of successive differences between intervals
RR	Interval between two successive R waves, s
RSA	Respiratory sinus arrythmia
S	ECG wave representing the final depolarization of the ventricles
SCG	Seismocardiography
SDNN	Standard deviation of NN intervals
SV	Stroke volume, ml
S1	First heart sound
S2	Second heart sound
S3	Third heart sound
S4	Fourth heart sound
ULF	Ultra-low frequency
VLF	Very low frequency
$\mathsf{\kappa }$	Proportionality factor in SV formula, given by Starr