Is It Safe To Split Higher Dosage Of Cardizem To Lower Dosage?

I presently take 180mg of cardizem in the morning. I also take 90mg of cardizem at night. I have been at the ER for a-fib several times in 8 days. Since no pharmacy had the 90mg on stock, I split the 180mg capsule. Is this ok? I am a 68 yr old woman with heart failure, diabetes, chronic disease anemia etc. I am 5 6 & weigh 323 lbs.