We examined the effects of blood flow-restricted, low-intensity resistance exercise (termed kaatsu), using an elastic band for resistance, on muscle activation in patients with cardiovascular diseases. Six patients with cardiovascular diseases [male, 69±12 (SD) years old, five old myocardial infarction and one dilated cardiomyopathy] performed biceps flexion exercises (four sets) using an elastic band for resistance with blood flow restriction [BFR (kaatsu training)] or CON (unrestricted blood flow). During a BFR (kaatsu training) session, subjects wore a kaatsu belt inflated to 110-160 mmHg on the proximal region of both arms. Surface electromyography (EMG) was recorded from the biceps brachii muscles, and mean integrated EMG (iEMG) was analyzed. Ratings of perceived exertion (RPE) were measured using the Borg scale immediately after the last set of each exercise (Post). During exercises, muscle activation increased progressively under BFR (kaatsu training) (approximately 40%), but not under CON; muscle activation was higher under BFR (kaatsu training) than that under CON in all exercises (P < 0.001). RPE at Post was also higher (P < 0.05) under BFR (kaatsu training) than that under CON in all exercises. RPE at Post was significantly correlated with increased iEMG in biceps flexion exercises (r = 0.68, P < 0.001). We conclude that kaatsu training using elastic bands for resistance enhances muscle activation in patients with cardiovascular diseases and may be an effective method to promote muscle hypertrophy in patients with cardiovascular diseases.