C. GRANT LA FARGE AND W. F. BERNHARD 
87 
Figure 7. — Low power photomicrograph of myocardium from a calf 21 days after microsphere induction of diffuse, 
ischemic infarction. Normal and hypertrophied myocardium (upper left) is adjacent to necrosis (center) diffuse 
round cell infiltrate and replacement of myofibrils with fibroblasts. Latex microspheres (6-14 microns diam- 
eter) are evident. 
nance of ventricular pressures at 0 mniHg. 
Thus, the microsphere failure model is, so 
far, the one most useful for an evaluation of 
long-term mechanical ventricular support or 
bypass systems. The normal state is followed 
by acute failure ; this, in turn, yields to a chronic 
failure state, gradually compensating by myo- 
cardial hypertrophy. The disadvantage of the 
model is that it does not resemble the principal 
clinical source of acute and chronic failure: 
major coronary artery disease. A reproducible 
model for that state has yet to be generated. 
It does, however, represent well the clinical 
state of diffuse, small-vessel coronary artery 
disease. 
While the microsphere failure model has 
proved the most useful for hemodynamic eval- 
uation, there is a distinct role for the total heart 
failure model of ventricular fibrillation. It rep- 
resents the "acid test" of the combined animal- 
pump system : not only is the "failure" complete, 
but the myocardium is consuming large quan- 
tities of energy, and is in a contracted state 
(resembling end-systole). The latter quality 
provides a small end-diastolic volume for a 
mechanical device to draw upon, and serves 
as a limiting factor in total "cardiac" (pump) 
output. In fact, the pump must draw also upon 
the atrium. 
One of the more fascinating observations in 
the studies of failure and fibrillation reported 
here, and previously, is the extent to which a 
mechanical pump, with its inflow tube in the 
left ventricle, draws upon the left atrium di- 
