Running and rowing are both great cardio workouts, but they affect the heart in different ways. Rowing is a whole-body exercise that works multiple muscle groups and requires the heart to circulate more blood efficiently. This can result in a stronger heart with greater stroke volume and reduced resting heart rate. Running mostly engages the legs and produces more extreme peaks in heart rate, particularly at high intensities during sprinting. Though both activities lower the risk of heart disease, rowing is low-impact and thus less stressful on joints. World-class rowers also tend to have bigger hearts than runners, indicating the special stress that rowing places on cardiac function.
Source: Live Science, NewsBytes, Shokz AU