I need more information to answer your questions.
What is the brand name or generic name of the blood pressure pill?
What is the dose of the pill (mg)?
How long ago did he eat the pills?
Enalapril is used in dogs. The usual dose is 0.25mg/lb of body weight. A 10 mg dose (2 - 5 mg pills) would be a normal dose for a 40 pound dog. If your dog is in that weight range, it should be safe, but you should keep him quiet for the day (no playing, running or long walks).
ost pitbulls are in that weight range. Do you know how much your dog weights.
I will follow up shortly with info on inducing vomiting with either hydrogen peroxide or salt.
The most readily available methods to induce vomiting at home are:
Side effects are rarely seen with normal dose levels. Rare side effects include low blood pressure, decreased appetitive, vomiting and diarrhea.
Even with excessive dosing, toxic effects are rare. None were reported in dogs given 36 times the recommended dose.
Your plan to keep an eye on him should be sufficient. There is not a need to induce vomiting.