I'm 34. I just terminated a pregnancy due to trisomy 21 and imminent heart failure. Can I still have a healthy baby or does this mean my chances r low?

Would consult .. A genetics expert and a high risk ob/gyn dr to give a full risk profile.
Healthy baby. There is dtill an excellent chance to have a normal baby. Good luck.
Sorry for your loss. Having one pregnancy with a trisomy (21) will generally add 1% to your future risk of any chromosome defect. Add that to about 1% for your age. Any pregnant woman has ~4% risk of some unexpected outcome (premi, defect, infection,etc.) Add it up and you have 94% chance of a good outcome if you try now. Please consult with a medical geneticist who can explore both family trees to find all your risks.