Effect of activity on supraventricular tachyarrhythmias after coronary artery bypass surgery. The purpose of this study was to evaluate patient activities, professional staff activities, backrest position, and diurnal variations as factors that may contribute to the onset of supraventricular tachyarrhythmias (SVT) after coronary artery bypass surgery (CABG). The activities surrounding the recognition of first-onset SVT, as well as preoperative and postoperative data and patient characteristics were examined in 249 patients having CABG. One hundred seventy-three patients qualified for the study; 28% of these patients (n = 49) had SVT. No statistical difference was found between the subjects with SVT and those without SVT when sex, cross-clamp time, creatine kinase peak, hemoglobin and hematocrit levels, and number of bypasses were examined. Patients who had SVT were older than those who did not: 64.8 years for the SVT group versus 60.7 years for the non-SVT group (p less than 0.01). SVT was rare in the first 24 hours after surgery, whereas 60% of the cases occurred during the next 48 hours, without significant diurnal variation: mean time of onset was 11:50 AM. No particular activity of the patient or nurse influenced the onset of SVT during the postoperative period in this group. 