I am a 59 year old male who has been lifting weights for 40 years. After having hiatal hernia surgery, should I continue to lift heavy weights?

What does your doctor have to say about it? Obviously, you shouldn't strain anything while you're healing, but I imagine that once you heal, you'll be all right.

As long as your technique is solid and you don't Valsalva (which you shouldn't do anyways), I think you'll be okay.

But again, ask your doctor.

What strength excercises should be done for swimmers

The easiest way I've found to strength train for specific endeavors is to mimic whatever you do in the sport itself.

So when you think of swimming, you think of the stages of each race:

To improve your start, train your quadriceps and calves so that they are as powerful and explosive as possible.

To improve your kick, train your hamstrings and lower back to be powerful, yet still maintain endurance.

To improve your upper-body strokes, focus on the core muscles and the stabilizer muscles that come into play during whatever stroke you perform. Your prime-mover muscles (the ones that do the bulk of the work) can then be built after you've formed a solid foundation with the core muscles and stabilizers.