Why is my dad's ECG abnormal during jogging?

What can cause chest pain during jogging. My dad was complaining of this. The doctor performed blood tests and ECG and it was normal. ECG was showing slight bradycardia but the dr said its normal as he was fasting. After the test results the dr referred him to a cardiologist to do stress test just in case. His ECG was abnormal. I want to know if this is a major abnormality and what can be the cause and possible treatment options. I know it’s too early to say anything but I just want you to tell me what possible condition it can be and if it’s a big deal or not. I have a picture of his ECG. He will have other tests done but I just want to know for the peace of my mind.