OBJECTIVE: To assess the efficacy of a strategy, based on telephone support oriented by accelerometer measurements, on the adherence to physical activity (PA) recommendations in cardiac patients not achieving PA recommendations. DESIGN: Prospective and randomized study. SETTING: A cardiac rehabilitation program (CRP) at a clinic. PARTICIPANTS: Stable, noncompliant cardiac (coronary artery disease, heart failure, post-cardiovascular surgery) patients (weekly moderate-intensity PA <150 min) were randomly assigned to an intervention group (n=19) or a control group (n=10). INTERVENTIONS: The intervention group wore an accelerometer for 8 weeks. Every 15 days, feedback and support were provided by telephone. The control group wore the accelerometer during the 8th week of the intervention only. MAIN OUTCOME MEASURES: Active energy expenditure (EE) (in kilocalories) and the time spent doing light, moderate, or intense PA (minutes per week). RESULTS: In the intervention group, the time spent at moderate-intensity PA increased from 95.6+/-80.7 to 137.2+/-87.5 min/wk between the 1st and 8th week (P=.002), with 36.8% of the sample achieving the target amount of moderate-intensity PA. During the 8th week, the EE averaged 543.7+/-144.1 kcal and 266.7+/-107.4 kcal in the intervention group and control group, respectively (P=.004). CONCLUSIONS: Telephone support based on accelerometer recordings appeared to be an effective strategy to improve adherence to PA in noncompliant patients. This intervention could be implemented after a CRP as an inexpensive, modern, and easy-to-use strategy.