I take 50mg atenolol on a split dose. Sometimes I get slight headache and heart rate is 58-60 mainly at night. Is this ok? Or the dose is too strong?

Depends. Would need to know why you are taking atenolol. Generally 25 mg of atenolol twice a day is a common dose. The slowing of heart to 58-60 would be expected. Headache is one of the non serious side effects known to be caused by atenolol. It is usually given as a once a day pill, tho it can be given twice a day. But u should check with ur doc since he/she knows ur case.