Does Stopping The Diuretic Further Declines The Heart Condition?

Heart Problems.
Hi My Dad has had two episodes of Vtach in the past week. He had a similar episode in sept. 2013. His blood pressure is higher than normal (140/89) which fluctuates, and his potassium is low. He is currently on a diuretic that his doctor wants him to stop, as his body does not have enough potassium. Since his heart is already weakened and been through trauma. Will halting the diuretic (i.e. less fluid in his body) only serve to weaken the heart?

Is there a survival rate for this? When in Vtach his heart went up to 250

He has never smoked. No family history of heart issues. Low sodium intake. Not sure what is causing this.