Re: What's the strongest muscle, the heart or the tongue?

You make an excellent point, Janelle.  

I, too, would guess that heart muscle would
be stronger than tongue.  The way to test
this would be to attach each muscle to a 
force transducer (which tells how hard
the muscle pulls) and stimulate the muscle
electrically to cause contraction.  

Unfortunately, I cannot find any evidence that
this exact experiment has actually been done, or 
at least the results published.  Ideally, the
two muscles would come from the same animal, since
hearts and tongues could vary widely.  In humans,
for example, tongue strength and endurance is
increased in trained speakers, trumpet players, etc.
Obviously, heart strength and endurance would be
increased in aerobically fit individuals.

Heart muscle is, indeed, considered muscle, albeit
a different 'type' than tongue muscle.  There are three
types of muscle: striated/skeletal, cardiac, smooth.
Tongue is striated muscle, like almost all of the
muscles under voluntary control.  Heart muscle
is cardiac.  Smooth muscles typically control things
that are involuntary and squeeze: our guts, arteries, etc.

Strength and endurance are two different measurements, 
as you point out.  And they refer to what you'd expect:
Strength is how hard you pull, endurance is how long
you can keep it up.  Interestingly, the endurance contest
is won by smooth muscle, which appears specially optimized
for very long hard contractions.  Next, of course, would
be cardiac (heart) muscle, followed by striated muscle, 
which would vary a lot depending on the particular muscle. 

But your question is about strength of tongue vs. heart.  
The answer to that, I really don't know.  If we're lucky,
someone will read this who has done the experiment, or do it,
and tell us both.

Incidentally, to perhaps confuse the issue further, 
this website claims that
"...the strongest muscle of all is the masseter muscle of your inner jaw",
and, for an alternate answer, 

this other website claims that "the muscles that can be considered to be the 
strongest in the body,[are] those of the lower body, since, these muscles receive 
the most strenous work of any muscles"