I had open heart surgery n may this year to replace my pulmonary valve. with a bovine tissue valve. when would it be safe to start trying for a baby?

Ask cardiologist!: Too complicated to answer without knowing why the valve was replaced, what is the condition of your heart, what meds you are on, how old you are, etc. Ask the surgeon and/or your cardiologist.

Check first: My guess would be that it would be ok, but you should check with your cardiologist first. There are many issues to consider. Your overall health; what medicines you are taking and which ones you can stop. How well does your heart function. What is the anatomy of your heart. There are more than one reason that you need an artificial valve. Your cardiologist is in the best position to answer you.

Depends : This depends on other factors like your heart function, other valve problems etc. But assuming everything is well, you could likely start trying now. But again, your safety depends on many other factors so please discuss this with your cardiologist.