• no mutants live for more than 24 hours, with the majority either stillborn or dying within the first few hours of life

• exhibit a small, but significant, increase in atrial size and atrial wall thickening

• neonatal and adult hearts show myocellular disorganization and degeneration

• exhibit about 8-10% fewer myocytes than controls

• neonatal and adult hearts show myocellular degeneration

• mean length and midpoint width of quiescent ventricular cardiac myocytes are 15 and 13% smaller, respectively, than in controls and mean myocyte area is decreased by 17%

• neonatal and adult hearts show myocellular disorganization

• heart weight to body weight ratio shows an 18-27% decrease in heart mass at 4-5 months of age, restricted to the left ventricle

• exhibit a 17% decrease in left ventricular mass

• altering the physiologic load on the heart shows some impairment in contractility

• at a baseline workload, hearts exhibit a 25% decrease in the maximal rate of relaxation

• hearts show a moderately good correlation of +dP/dT to increased work, however the slope of the Starling curve is severely decreased during relaxation suggesting that hearts cannot respond to an increased work load by shortening their relaxation time

• isolated adult cardiac myocytes and hypersensitive to calcium; addition of calcium led to immediate cellular hypercontracture and death

• neonatal and adult hearts show myocellular disorganization and degeneration

• exhibit about 8-10% fewer myocytes than controls

• neonatal and adult hearts show myocellular degeneration

• mean length and midpoint width of quiescent ventricular cardiac myocytes are 15 and 13% smaller, respectively, than in controls and mean myocyte area is decreased by 17%

• altering the physiologic load on the heart shows some impairment in contractility

• at a baseline workload, hearts exhibit a 25% decrease in the maximal rate of relaxation

• hearts show a moderately good correlation of +dP/dT to increased work, however the slope of the Starling curve is severely decreased during relaxation suggesting that hearts cannot respond to an increased work load by shortening their relaxation time