Are there risks involved with cardiac rehab programs?

Minimal. Cardiac rehab is conducted under EKG monitoring just like in a hospital. The majority of patients have undergone angioplasty/stent placement or bypass surgery. Such patients have been "revascularized." prior to being enrolled in rehab, a patient has a stress test to be certain there are no significant signs of ischemia (inadequate blood flow to the heart muscle). Rehab strengthens the heart.
No mucho. It's a supervised and graduated program designed for people with heart disease or recent heart surgery. It's very safe. But, hey, awakening every morning carries risk too!