Echocardiography is an area that is far outside the realm of my specialty.
However, the following reference may be of help to your vet:
 
Vet Radiol Ultrasound 2000 Sept-Oct;41(5):452-6 Related Articles, Books
 
M-mode and Doppler echocardiographic findings in normal ferrets
sedated with ketamine hydrochloride and midazolam.
 
Stepien RL, Benson KG, Wenholz LJ.
 
Department of Medical Sciences, University of Wisconsin School of
Veterinary Medicine, Madison 53706, USA.
 
M-mode and Doppler echocardiographic values were obtained from 30 normal
adult ferrets (14 neutered females, 13 neutered males, 3 intact males)
sedated with an intramuscular combination of ketamine hydrochloride and
midazolam.  Routine M-mode measurements of the left and right ventricle,
left atrium (LA) and aorta (AO) and Doppler measurements of aortic and
pulmonic outflow, and mitral inflow were recorded.  The following values
were calculated: LA:AO diameter, ratio of peak E: peak A wave velocity
(E:A ratio) for mitral inflow, and stroke volume (SV), cardiac output
(CO) and cardiac index (CI) for both pulmonary and aortic outflow tracts.
Maximal aortic velocities (AOmax) and velocity-time integral values (AO
VTI) were significantly less than corresponding pulmonary outflow tract
values (PAmax, PA VTI) but there was no difference in calculated values
for SV, CO or CI.  Calculated CO values were in the range expected based
on the size of the species.  Difficulties in aligning the aortic outflow
tract for Doppler imaging may make pulmonary outflow Doppler values more
consistent for use in estimating volume flow in ferrets.
 
I would submit that the calculated values in this paper would be what you
are looking for.
 
With kindest regards,
Bruce Williams, DVM
 
[Original post in the FHL contains further information; see the website
http://groups.yahoo.com/group/Ferret-Health-list to learn that.]
[Posted in FML issue 3460]